NAD-dependent histone deacetylase HST3, a member of the sirtuin family. Catalyzes deacetylation of histone H3 lysine 56 (H3K56), a critical residue in nucleosome assembly during DNA replication and repair. Functions redundantly with HST4 in regulating transcription, sister chromatid recombination, DNA damage checkpoint control, and genome stability.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005634
nucleus
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: HST3 localizes to the nucleus where it functions as a histone deacetylase. UniProt subcellular localization states both cytoplasm and nucleus. This IBA annotation is supported by phylogenetic inference from orthologs. IC evidence from PMID:12242223 also confirms nuclear localization, which is essential for its function in histone deacetylation and transcriptional regulation.
Reason: HST3 is a nuclear protein required for histone H3K56 deacetylation during S/G2 phase transitions (PMID:17977840). IBA annotation is well-supported by orthologous relationships across sirtuins and confirmed experimentally.
Supporting Evidence:
PMID:12242223
Furthermore, Hst3 was physically present at 2mu ARS in a silencing context as well as at the endogenous 2mu plasmid
|
|
GO:0017136
histone deacetylase activity, NAD-dependent
|
IBA
GO_REF:0000033 |
MODIFY |
Summary: This parent term captures the correct NAD-dependent histone deacetylase chemistry, but HST3s core characterized activity is the more specific H3K56 deacetylase activity. Multiple experimental lines of evidence support the H3K56 substrate specificity.
Reason: The annotation should use the current specific child term for HST3s demonstrated NAD-dependent histone H3K56 deacetylase activity.
Proposed replacements:
histone H3K56 deacetylase activity, NAD-dependent
Supporting Evidence:
PMID:17977840
Hst3 has NAD-dependent histone deacetylase activity in vitro and that it functions during S phase to deacetylate the core domain of histone H3 at lysine 56 (H3K56)
file:yeast/HST3/HST3-deep-research-falcon.md
Falcon literature synthesis supports HST3 as an NAD-dependent H3K56 deacetylase.
PMID:23357952
These functions are necessary for the repair of replication-born DSBs by SCR
|
|
GO:0000183
rDNA heterochromatin formation
|
IBA
GO_REF:0000033 |
KEEP AS NON CORE |
Summary: HST3 contributes to rDNA heterochromatin formation through its NAD-dependent histone deacetylase activity. However, this term appears somewhat over-specific compared to the broader silencing roles. UniProt documents roles in histone H3K56 deacetylation and telomeric silencing. The rDNA-specific annotation is less well-established than general transcriptional silencing.
Reason: While HST3 participates in silencing processes that may include rDNA, this is not explicitly demonstrated as a core function. The primary characterized substrate is histone H3K56, which affects broader transcription and genome stability. The rDNA-specific function is an inferred application of the deacetylase activity rather than a primary function.
Supporting Evidence:
PMID:7498786
The SIR2 gene family, conserved from bacteria to humans, functions in silencing, cell cycle progression, and chromosome stability.
PMID:31167142
Yeast Sirtuin Family Members Maintain Transcription Homeostasis to Ensure Genome Stability.
|
|
GO:0000781
chromosome, telomeric region
|
IEA
GO_REF:0000108 |
KEEP AS NON CORE |
Summary: This is a localization annotation indicating HST3 associates with telomeric regions of chromosomes. Evidence shows HST3 and HST4 contribute to telomeric silencing (PMID:7498786), but this is inferred primarily from functional effects rather than direct localization studies. The IEA inference from GO:0031509 (subtelomeric heterochromatin formation) is logically sound.
Reason: HST3 function at telomeric regions is secondary to its core H3K56 deacetylase activity. The localization annotation is supported by functional genomics (silencing phenotypes) but this is not a primary function description. Better captured under heterochromatin formation processes.
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: Duplicate of annotation 1 (same GO term, different evidence code). UniProtKB subcellular location vocabulary explicitly states HST3 is localized to nucleus and cytoplasm. This IEA annotation from UniProt is consistent with the IBA annotation.
Reason: Redundant but valid annotation. Multiple evidence types (IEA from subcellular location mapping and IBA from phylogenetics) support nuclear localization.
|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: UniProtKB subcellular location states "Cytoplasm. Nucleus." HST3 is documented in both compartments, though primary function is nuclear. Cytoplasmic localization is less characterized but appears to be a minor component of HST3 localization.
Reason: HST3 has documented cytoplasmic localization in UniProt, but its characterized functions (H3K56 deacetylation, transcription regulation, DNA repair) are nuclear. Cytoplasmic localization may represent transit or peripheral functions.
|
|
GO:0006351
DNA-templated transcription
|
IEA
GO_REF:0000043 |
MODIFY |
Summary: HST3 involvement in transcription is experimentally confirmed. PMID:31167142 demonstrates that Hst3 and Hst4 regulate transcription homeostasis by repressing nascent RNA transcription at many loci. This prevents excessive transcription-associated R-loops that cause DNA damage. The function is broader than suggested by general "DNA-templated transcription" term.
Reason: HST3 is documented as repressing transcription through H3K56 deacetylation. IEA from UniProt keywords (Transcription) is supported by experimental evidence (PMID:31167142 shows HST3 and HST4 repress nascent transcription), but the more informative GO term is negative regulation of DNA-templated transcription.
Proposed replacements:
negative regulation of DNA-templated transcription
Supporting Evidence:
PMID:31167142
Hst3 and Hst4 are required to repress transcription of coding and non-coding RNAs
|
|
GO:0016740
transferase activity
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: Transferase activity is an extremely broad parent term, but it is not mechanistically wrong for class III/NAD-dependent deacetylases: the acetyl group is transferred to NAD during the sirtuin reaction. It is much less informative than the H3K56-specific deacetylase term.
Reason: GO:0016740 is a valid broad superclass for NAD-dependent deacetylase chemistry, but HST3s core molecular function is better captured by GO:0140765 histone H3K56 deacetylase activity, NAD-dependent.
|
|
GO:0017136
histone deacetylase activity, NAD-dependent
|
IEA
GO_REF:0000117 |
MODIFY |
Summary: Duplicate parent-term annotation for NAD-dependent histone deacetylase activity. The biology is valid, but the stronger HST3-specific review should point to H3K56 deacetylase activity.
Reason: Use the specific child term GO:0140765 for HST3s demonstrated H3K56 deacetylase activity.
Proposed replacements:
histone H3K56 deacetylase activity, NAD-dependent
|
|
GO:0031507
heterochromatin formation
|
IEA
GO_REF:0000117 |
KEEP AS NON CORE |
Summary: HST3 contributes to heterochromatin formation through histone deacetylation. PMID:7498786 shows hst3 hst4 double mutants are defective in telomeric silencing. However, PMID:31167142 suggests the primary mechanism is regulation of transcription homeostasis rather than structural heterochromatin formation. The term is somewhat over-general for the more specific H3K56 deacetylation function.
Reason: While HST3 participates in silencing and heterochromatin-associated processes, its primary characterized function is H3K56 deacetylation and transcription regulation. Heterochromatin formation is an inferred downstream consequence rather than direct function.
|
|
GO:0034979
NAD-dependent protein lysine deacetylase activity
|
IEA
GO_REF:0000120 |
KEEP AS NON CORE |
Summary: This is a correct but broad parent term for NAD-dependent protein lysine deacetylase chemistry. HST3s characterized substrate is histone H3 lysine 56, so the parent term should not be promoted as the core MF.
Reason: The annotation is not wrong, but GO:0140765 is the informative core molecular-function term for HST3.
|
|
GO:0046872
metal ion binding
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: HST3 contains zinc-binding sites. UniProt specifically documents that HST3 binds 1 zinc ion per subunit, with 4 zinc-coordinating residues in the catalytic sirtuin domain (positions 195, 198, 220, 223). The annotation is inferred from UniProt keyword "Zinc" (GO_REF:0000043 is UniProt-KW mapping). PMID:30358795 on yeast zinc proteome may provide additional validation.
Reason: HST3 contains a zinc cofactor essential for sirtuin catalytic activity. The annotation is well-supported by UniProt feature annotations identifying zinc-binding residues.
|
|
GO:0070403
NAD+ binding
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: HST3 is an NAD-dependent deacetylase and must bind NAD+ cofactor. UniProt documents multiple NAD+-binding residues (positions 60-79, 151-154, 282-284, 312-314, 333) in the characteristic sirtuin NAD+ binding domain. The inference from InterPro IPR003000 (sirtuin domain) is appropriate. This is a required cofactor binding activity.
Reason: Essential cofactor binding for catalytic activity. HST3 catalytic mechanism absolutely requires NAD+ binding. The annotation is correctly inferred from the sirtuin domain structure.
|
|
GO:0008270
zinc ion binding
|
RCA
PMID:30358795 The cellular economy of the Saccharomyces cerevisiae zinc pr... |
ACCEPT |
Summary: Zinc ion binding is specifically documented by UniProt with four coordinating residues identified through structure. RCA (Reviewed Computational Analysis) using PMID:30358795 (yeast zinc proteome characterization) is appropriate evidence. This is equivalent to the metal ion binding annotation but more specific.
Reason: Specific instance of the broader metal ion binding annotation. Zinc is specifically required for sirtuin catalytic activity. RCA evidence from zinc proteome characterization is valid.
Supporting Evidence:
PMID:30358795
The cellular economy of the Saccharomyces cerevisiae zinc proteome.
|
|
GO:0005634
nucleus
|
IC
PMID:12242223 A novel yeast silencer. the 2mu origin of Saccharomyces cere... |
ACCEPT |
Summary: Third annotation of nuclear localization. PMID:12242223 provides experimental evidence that HST3 is physically present at the 2mu ARS silencer element in a silencing context, inferred curated evidence (IC) of nuclear localization. Redundant with annotations 1 and 5.
Reason: Valid experimental evidence of nuclear localization through physical presence at genomic elements. Redundant with other nuclear localization annotations but valid.
Supporting Evidence:
PMID:12242223
Furthermore, Hst3 was physically present at 2mu ARS in a silencing context as well as at the endogenous 2mu plasmid
|
|
GO:0031509
subtelomeric heterochromatin formation
|
IGI
PMID:7498786 The SIR2 gene family, conserved from bacteria to humans, fun... |
ACCEPT |
Summary: PMID:7498786 shows that hst3 hst4 double mutants are defective in telomeric silencing, establishing that HST3 and HST4 contribute together to subtelomeric silencing. IGI (Inferred from Genetic Interaction) is appropriate evidence code, using HST4 as the interacting gene. This demonstrates HST3 function in telomeric silencing.
Reason: Experimental evidence demonstrates HST3 requirement for subtelomeric silencing. The function is well-characterized even if redundant with HST4. This is a core genomic stability function.
Supporting Evidence:
PMID:7498786
hst3 hst4 double mutants are defective in telomeric silencing
|
|
GO:0017136
histone deacetylase activity, NAD-dependent
|
IDA
PMID:17977840 Hst3 is regulated by Mec1-dependent proteolysis and controls... |
MODIFY |
Summary: IDA evidence from PMID:17977840 directly supports the specific H3K56 NAD-dependent deacetylase activity, not just the parent histone deacetylase term.
Reason: The direct assay evidence should be represented with GO:0140765, the specific H3K56 child term.
Proposed replacements:
histone H3K56 deacetylase activity, NAD-dependent
Supporting Evidence:
PMID:17977840
Hst3 has NAD-dependent histone deacetylase activity in vitro and that it functions during S phase to deacetylate the core domain of histone H3 at lysine 56 (H3K56)
|
|
GO:0017136
histone deacetylase activity, NAD-dependent
|
IMP
PMID:17977840 Hst3 is regulated by Mec1-dependent proteolysis and controls... |
MODIFY |
Summary: IMP evidence from PMID:17977840 supports the specific H3K56 deacetylase function: loss of Hst3 causes failure to regulate H3K56 acetylation and downstream checkpoint/cohesion phenotypes.
Reason: The mutant phenotype evidence should be represented with GO:0140765 rather than only the parent NAD-dependent histone deacetylase term.
Proposed replacements:
histone H3K56 deacetylase activity, NAD-dependent
Supporting Evidence:
PMID:17977840
Loss of Hst3-mediated regulation of H3K56 acetylation results in a defect in the S phase DNA damage checkpoint
|
|
GO:0006351
DNA-templated transcription
|
IDA
PMID:31167142 Yeast Sirtuin Family Members Maintain Transcription Homeosta... |
MODIFY |
Summary: IDA evidence from PMID:31167142 shows comprehensive transcriptomic analysis demonstrating HST3 directly regulates transcription. Using NET-seq (native elongating transcript sequencing), the authors show that loss of Hst3 and Hst4 leads to global increases in nascent transcription at ~1,000 genes. This is direct measurement of transcription dynamics, not merely inference. Highly specific to H3K56-mediated regulation.
Reason: Robust experimental evidence supports transcriptional repression: NET-seq shows increased nascent transcription when HST3/HST4 are lost. The parent DNA-templated transcription term should be replaced by the more precise negative regulation term.
Proposed replacements:
negative regulation of DNA-templated transcription
Supporting Evidence:
PMID:31167142
Loss of Hst3 and Hst4 led to a global shift in the nascent RNA transcriptome, with an average fold increase of ~1.4
|
|
GO:0009299
mRNA transcription
|
IDA
PMID:31167142 Yeast Sirtuin Family Members Maintain Transcription Homeosta... |
MODIFY |
Summary: PMID:31167142 demonstrates that HST3 negatively regulates RNA polymerase II mRNA transcription: metagene analysis shows higher nascent transcript levels throughout genic regions, especially near transcription start sites, when HST3/HST4 activity is lost.
Reason: Direct NET-seq evidence shows mRNA-coding regions are specifically affected, but the direction is repressive rather than neutral participation in mRNA transcription. The annotation should therefore use a negative regulation child term consistent with the GO:0006351 reviews from the same paper.
Proposed replacements:
negative regulation of transcription by RNA polymerase II
Supporting Evidence:
PMID:31167142
Metagene plots of mean nascent transcript levels, representative genome browser views of NET-seq data, and a heatmap of the log2-fold change between the hst4ฮ HST3-FRB mutant and WT confirmed higher levels of transcription throughout genic regions
|
|
GO:1990414
replication-born double-strand break repair via sister chromatid exchange
|
IMP
PMID:23357952 Histone H3K56 acetylation, Rad52, and non-DNA repair factors... |
ACCEPT |
Summary: PMID:23357952 provides comprehensive evidence that HST3 is required for sister chromatid recombination (SCR) of replication-born double-strand breaks. The authors identify hst3 among 12 mutants consistently impaired in SCR using physical assay of recombination. Loss of HST3 (and HST4) severely impairs the ability to repair DSBs with the sister chromatid, with 50-fold decrease in intrachromosomal SCR. This is a major genome stability function dependent on H3K56 acetylation state.
Reason: HST3 is a critical factor for proper DSB repair template choice (sister chromatid preference). Loss results in genome instability and increased recombination with homologs instead of sister chromatids. Core function in genome stability.
Supporting Evidence:
PMID:23357952
The hst3ฮ mutation is strongly affected in intrachromosomal SCR repeat recombination (50-fold decrease)
|
|
GO:0046459
short-chain fatty acid metabolic process
|
IMP
PMID:12618394 Short-chain fatty acid activation by acyl-coenzyme A synthet... |
MARK AS OVER ANNOTATED |
Summary: PMID:12618394 shows that growth on short-chain fatty acids (acetate, propionate) is severely impaired in quintuple sir2 hst1 hst2 hst3 hst4 mutant strain, with HST3 and HST4 identified as most important for growth on these substrates. However, this is not the primary function of HST3. The mechanism appears to involve SIR2 family proteins controlling acetyl-CoA synthetase (Acs) enzyme activity, suggesting an indirect metabolic role rather than direct involvement in lipid metabolism.
Reason: While HST3 contributes to growth on short-chain fatty acids through its requirement for Acs activity regulation, this is not a primary enzymatic function. HST3 is a histone deacetylase whose role in fatty acid metabolism is indirect, mediated through NAD-dependent regulation of Acs protein acetylation. The annotation overstates HST3s direct involvement in metabolic process. Better annotated as a regulatory cofactor effect than a metabolic process function.
Supporting Evidence:
PMID:12618394
Short-chain fatty acid activation by acyl-coenzyme A synthetases requires SIR2 protein function in Salmonella enterica and Saccharomyces cerevisiae.
|
provider: falcon
model: Edison Scientific Literature
cached: false
start_time: '2026-05-04T11:10:20.483840'
end_time: '2026-05-04T11:19:33.426148'
duration_seconds: 552.94
template_file: templates/gene_research_go_focused.md
template_variables:
organism: yeast
gene_id: HST3
gene_symbol: HST3
uniprot_accession: P53687
protein_description: 'RecName: Full=NAD-dependent histone deacetylase HST3; EC=2.3.1.286
{ECO:0000255|PROSITE-ProRule:PRU00236}; AltName: Full=Homologous to SIR2 protein
3; AltName: Full=Regulatory protein SIR2 homolog 3;'
gene_info: Name=HST3; OrderedLocusNames=YOR025W; ORFNames=OR26.15;
organism_full: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
protein_family: Belongs to the sirtuin family. Class I subfamily.
protein_domains: DHS-like_NAD/FAD-binding_dom. (IPR029035); NAD-dep_sirtuin_deacylases.
(IPR050134); Sirtuin. (IPR003000); Sirtuin_cat_small_dom_sf. (IPR026591); Ssirtuin_cat_dom.
(IPR026590)
provider_config:
timeout: 600
max_retries: 3
parameters:
allowed_domains: []
temperature: 0.1
citation_count: 29
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'HST3' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene HST3 (gene ID: HST3, UniProt: P53687) in yeast.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'HST3' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene HST3 (gene ID: HST3, UniProt: P53687) in yeast.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The literature extracted in this run consistently defines Hst3 as a budding yeast sirtuin-family, NAD+-dependent histone deacetylase thatโtogether with its paralog Hst4โerases histone H3 lysine 56 acetylation (H3K56ac). Key primary evidence comes from S. cerevisiae studies explicitly using HST3/HST4 deletion strains, H3K56 mutant histones, and Hst3-tagged expression time courses during the cell cycle and after DNA damage (maas2006cellcycleand pages 8-9, maas2006cellcycleand pages 2-3, maas2006cellcycleand pages 5-6). This functional profile matches the user-specified UniProt identity for HST3 (YOR025W; P53687) as an NAD-dependent histone deacetylase in the sirtuin family.
Hst3 belongs to the sirtuin class of deacetylases whose activity depends on NAD+; in vitro, recombinant/full-length Hst3/Hst4 require NAD+ to deacetylate H3K56ac and are inhibited by nicotinamide, consistent with canonical sirtuin biochemistry (delgoshaie2013studyofhistone pages 39-44). Functionally, this places Hst3 within metabolicโepigenetic coupling, since NAD+ availability can constrain enzymatic flux through deacetylation reactions.
H3K56ac is a cell-cycle regulated histone modification that is enriched in S phase (new histone deposition during DNA replication) and removed as cells enter G2/M (maas2006cellcycleand pages 5-6, maas2006cellcycleand pages 8-9). In wild-type logarithmically growing yeast, H3K56ac constitutes approximately ~20% of total H3, with most acetylated H3K56 present during S phase (maas2006cellcycleand pages 8-9).
Hst3 and Hst4 act as the primary โerasersโ of this mark: deletion of both enzymes increases H3K56ac by >4-fold (maas2006cellcycleand pages 8-9), and genetic epistasis experiments indicate H3K56 is the dominant functional substrate of Hst3/Hst4 (maas2006cellcycleand pages 1-2, maas2006cellcycleand pages 8-9).
Primary demonstrated enzymatic activity: Hst3 catalyzes deacetylation of acetylated histone H3 lysine 56 (H3K56ac) in an NAD+-dependent manner (maas2006cellcycleand pages 1-2, delgoshaie2013studyofhistone pages 39-44). Multiple lines of evidence support high substrate specificity and functional dominance of H3K56:
Several quantitative observations help bound the magnitude and kinetics of the mark:
H3K56ac is linked to replication-coupled chromatin assembly, and the timely removal of this mark by Hst3/Hst4 is required for genome integrity. In hst3ฮ hst4ฮ mutants, essentially all H3 becomes K56-acetylated throughout the genome and cell cycle, and this hyperacetylation is associated with replication-associated stress phenotypes and genome instability (delgoshaie2013studyofhistone pages 79-83, delgoshaie2013studyofhistone pages 75-79). The toxicity of excessive H3K56ac is further supported by the observation that many defects in hst3ฮ hst4ฮ cells are attenuated by H3K56R (delgoshaie2013studyofhistone pages 79-83).
A central theme in the literature is that Hst3 is itself regulated by DNA damage checkpoints, which tune H3K56ac levels during replication stress.
In the highly cited primary study by Maas et al. (Molecular Cell, July 2006; https://doi.org/10.1016/j.molcel.2006.06.006), Hst3 is downregulated by checkpoint signaling in response to replication stressors MMS and HU (maas2006cellcycleand pages 8-9, maas2006cellcycleand pages 2-3). Importantly:
Conceptually, this checkpoint-mediated repression is interpreted as adaptive: forced/constitutive expression of Hst3 reduces H3K56ac and makes cells more damage sensitive, and overexpression sensitizes growth on CPT in the cited work (maas2006cellcycleand pages 5-6, maas2006cellcycleand pages 8-9).
A 2023 review on yeast DSB chromatin (International Journal of Molecular Sciences, Feb 2023; https://doi.org/10.3390/ijms24043248) frames Hst3/Hst4 as key deacetylases of H3K56ac in DNA repair contexts and cites studies in which Mec1-dependent proteolysis of Hst3 links H3K56 deacetylation to S-phase checkpoint control and sister chromatid cohesion (frigerio2023thechromatinlandscape pages 23-24).
A 2023 review on mRNA homeostasis (Transcription, Feb 2023; https://doi.org/10.1080/21541264.2023.2183684) cites prior work linking Hst3 to transcriptional homeostasis through a functional interaction with the RNA exosome, positioning Hst3 beyond histone-only models and into coordination of transcription with RNA decay pathways (bryll2023thecircularlogic pages 8-9).
Hst3 is cell-cycle regulated, with highest expression in G2/M and low levels in G1 (maas2006cellcycleand pages 5-6, maas2006cellcycleand pages 2-3). In the Maas et al. time course experiments, H3K56ac peaks at ~30โ40 minutes after G1 release and then declines, consistent with Hst3 induction later in the cycle (maas2006cellcycleand pages 5-6).
A 2021 review synthesis of the H3K56ac field (Genes, Feb 2021; https://doi.org/10.3390/genes12030342) highlights a strong layer of post-translational regulation: Hst3 has a very short half-life (reported as ~8โ9 minutes in the cited synthesis), and mutation of key C-terminal phosphorylation sites can increase its half-life from ~8 minutes to 45 minutes, consistent with CDK/SCF-mediated degradation control (gershon2021theamazingacrobat pages 4-5). This complements the core 2006 checkpointโtranscription model by emphasizing rapid protein-level reset.
A 2024 proteome-wide study of ubiquitylation and DNA damage responses in yeast (Molecular & Cellular Proteomics, Jan 2024; https://doi.org/10.1016/j.mcpro.2023.100695) reiterates that Hst3 is โwell known to be rapidly degraded upon MMSโ and experimentally shows that when nuclear proteasome function is perturbed (anchor-away approach), Hst3 accumulates and is not degraded under rapamycin treatment in their turnover assays (blaszczak2024dissectingubiquitylationand pages 7-9). Although the authors did not capture Hst3 ubiquitination sites in their K-ฮต-GG enrichment dataset, they observed strong MMS-induced ubiquitination behavior for Hst4, highlighting paralog differences while reinforcing proteolysis as a regulatory axis (blaszczak2024dissectingubiquitylationand pages 7-9).
The evidence assembled here strongly supports Hst3 acting on chromatin-associated nuclear histone H3, because its primary substrate is H3K56ac and its phenotypes are chromatin/replication/checkpoint linked (maas2006cellcycleand pages 1-2, maas2006cellcycleand pages 8-9, delgoshaie2013studyofhistone pages 75-79). However, the specific excerpts retrieved in this run do not contain an explicit microscopy- or fractionation-based localization statement for Hst3 protein. Therefore, nuclear/chromatin site of action is inferred from substrate and pathway context rather than directly demonstrated within the extracted text (gershon2021theamazingacrobat pages 4-5).
HST3 is routinely used in yeast genetics and chromatin biology as a โcontrol knobโ for global H3K56ac abundance: deletion of HST3/HST4 drives hyperacetylation, while HST3 forced expression reduces the mark and can sensitize cells to replication stress (maas2006cellcycleand pages 5-6, maas2006cellcycleand pages 8-9). This enables tractable perturbation of replication-coupled chromatin maturation, checkpoint signaling, and genome stability mechanisms.
The 2024 Molecular & Cellular Proteomics work demonstrates a practical implementation: integrating protein turnover assays with nuclear proteasome perturbation to evaluate stress-triggered degradation programs, including Hst3 behavior during MMS response (blaszczak2024dissectingubiquitylationand pages 7-9). This situates Hst3 among proteins whose abundance is tuned by nuclear proteostasis during genotoxic stress.
A widely adopted conceptual application is the checkpoint logic documented by Maas et al.: replication stress represses HST3 so that H3K56ac persists during stress, supporting survival, whereas inappropriate Hst3 activity under stress is detrimental (maas2006cellcycleand pages 2-3, maas2006cellcycleand pages 6-8).
Expert synthesis in the 2021 review emphasizes that H3K56ac sits at a โbalance pointโ in genome maintenance: both insufficient acetylation (writer-side defects) and insufficient deacetylation (eraser-side defects) generate genome instability, and Hst3 is presented as the dominant deacetylase whose precise temporal control is essential (gershon2021theamazingacrobat pages 4-5).
Recent reviews (2023) reinforce this view by incorporating Hst3/Hst4 into broader chromatinโDDR frameworks (DSB chromatin landscape, pathway choice, checkpoint coupling), while also pointing to additional regulatory outcomes such as cohesion control (frigerio2023thechromatinlandscape pages 23-24).
Recent (2023โ2024) sources in this run mainly extend systems-level context rather than redefining enzymology:
The following table compiles the key functional-annotation points (identity, reaction, substrate specificity, regulation, phenotypes, and recent literature).
| Category | Summary | Key sources (year, journal, DOI URL) |
|---|---|---|
| Identity | HST3 / YOR025W / UniProt P53687 in Saccharomyces cerevisiae encodes an NAD+-dependent sirtuin-family histone deacetylase; evidence in the cited literature consistently places Hst3 with Hst4 as the principal erasers of H3K56 acetylation in budding yeast, with Hst3 as the dominant paralog under many conditions. (maas2006cellcycleand pages 1-2, maas2006cellcycleand pages 5-6, gershon2021theamazingacrobat pages 4-5) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Gershon & Kupiec, 2021, Genes, https://doi.org/10.3390/genes12030342 |
| Enzymatic activity/reaction | Hst3 catalyzes deacetylation of histone H3 lysine 56 acetylation (H3K56ac) in an NAD+-dependent reaction. Recombinant/full-length Hst3/Hst4 require NAD+ for H3K56 deacetylation in vitro; nicotinamide inhibits this activity, whereas TSA does not. De novo Hst3 expression in arrested cells causes rapid loss of H3K56ac, supporting direct enzymatic action. (delgoshaie2013studyofhistone pages 39-44, gershon2021theamazingacrobat pages 4-5) | Delgoshaie, 2013, thesis excerpts; Gershon & Kupiec, 2021, Genes, https://doi.org/10.3390/genes12030342 |
| Primary substrate specificity | The major demonstrated substrate is histone H3 acetylated at lysine 56. Multiple cited studies conclude that H3K56 is the major functional target: H3K56R is epistatic to phenotypes caused by HST3/HST4 deletion or HST3 overexpression, and loss of Hst3/Hst4 does not comparably elevate other H3/H4 N-terminal acetylation sites in the evidence summarized here. (maas2006cellcycleand pages 1-2, maas2006cellcycleand pages 8-9, delgoshaie2013studyofhistone pages 39-44) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Delgoshaie, 2013, thesis excerpts |
| Pathways/biological processes | Hst3 functions in the H3K56 acetylation cycle linked to DNA replication, replication-coupled chromatin assembly, DNA damage tolerance/repair, S-phase checkpoint control, sister chromatid cohesion, and genome stability. Reviews also connect H3K56ac/Hst3-Hst4 to chromatin restoration after repair; a 2023 transcription review further cites prior evidence that Hst3 interacts with the RNA exosome to support transcriptional homeostasis. (frigerio2023thechromatinlandscape pages 23-24, delgoshaie2013studyofhistone pages 44-48, delgoshaie2013studyofhistone pages 75-79, bryll2023thecircularlogic pages 8-9) | Frigerio et al., 2023, International Journal of Molecular Sciences, https://doi.org/10.3390/ijms24043248; Bryll & Peterson, 2023, Transcription, https://doi.org/10.1080/21541264.2023.2183684 |
| Cell-cycle regulation | H3K56ac accumulates in S phase and is removed as cells enter G2/M. Hst3 is low in G1, rises through the cell cycle, is highest in G2/M, and has a short half-life. Hst3 belongs to the CLB2 cluster of cell-cycle-regulated genes. C-terminal phosphorylation sites including T380/T384 form a phosphodegron promoting SCF-mediated turnover; mutation of these sites stabilizes Hst3. (maas2006cellcycleand pages 5-6, maas2006cellcycleand pages 2-3, delgoshaie2013studyofhistone pages 51-56, delgoshaie2013studyofhistone pages 113-118, gershon2021theamazingacrobat pages 4-5) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Gershon & Kupiec, 2021, Genes, https://doi.org/10.3390/genes12030342 |
| DNA damage checkpoint regulation | During replication stress/DNA damage, Hst3 is downregulated in a checkpoint-dependent manner so H3K56ac persists. In the evidence set, this requires Mec1 and Rad53, but not Dun1 or Crt1; repression is prominent with MMS and HU, but not with bleomycin/CPT in the Maas study. Later evidence summarized in reviews/thesis excerpts adds Mec1-dependent phosphorylation/proteolysis as a mechanism under stress. Overexpression or constitutive expression of HST3 increases DNA-damage sensitivity, implying that checkpoint-mediated HST3 repression is adaptive. (maas2006cellcycleand pages 2-3, maas2006cellcycleand pages 6-8, maas2006cellcycleand pages 8-9, delgoshaie2013studyofhistone pages 44-48, frigerio2023thechromatinlandscape pages 23-24) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Frigerio et al., 2023, International Journal of Molecular Sciences, https://doi.org/10.3390/ijms24043248 |
| Phenotypes when perturbed | hst3ฮ hst4ฮ causes constitutive H3K56 hyperacetylation and severe defects: slow growth, temperature sensitivity, transcriptional derepression at telomeres, chromosome segregation defects, high chromosome loss, spontaneous DNA damage/genome instability, reduced viability, and hypersensitivity to genotoxic stress (MMS/HU/CPT-related assays in the cited studies). Many defects are suppressed by H3K56R, indicating they arise from excess H3K56ac. HST3 overexpression inhibits growth in MMS and sensitizes cells to continuous CPT; a 2024 proteomics study used this known phenotype as a control. (maas2006cellcycleand pages 8-9, delgoshaie2013studyofhistone pages 79-83, blaszczak2024dissectingubiquitylationand pages 7-9, gershon2021theamazingacrobat pages 4-5) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Blaszczak et al., 2024, Molecular & Cellular Proteomics, https://doi.org/10.1016/j.mcpro.2023.100695 |
| Quantitative/statistical data points | Reported values in the gathered evidence include: ~20% of total H3 is H3K56-acetylated in log-phase WT cells; >4-fold increase in H3K56ac in hst3ฮ hst4ฮ; H3K56ac peaks ~30โ40 min after G1 release; after one cell cycle without Hst3, ~50% of histones carry H3K56ac; double-mutant G2/M-arrested cells reach ~98โ100% H3K56ac; Hst3 half-life is reported as ~15 min in Maas 2006 and ~8โ9 min, shortened to ~3.5 min under stress, in the 2021 review synthesis; phosphosite mutation can extend half-life from 8 min to 45 min. In Blaszczak 2024, Hst4 (not Hst3) showed >50-fold MMS-induced ubiquitylation at one site, whereas Hst3 ubiquitylation sites were not captured. (maas2006cellcycleand pages 8-9, maas2006cellcycleand pages 2-3, gershon2021theamazingacrobat pages 4-5, delgoshaie2013studyofhistone pages 51-56, blaszczak2024dissectingubiquitylationand pages 7-9) | Maas et al., 2006, Molecular Cell, https://doi.org/10.1016/j.molcel.2006.06.006; Gershon & Kupiec, 2021, Genes, https://doi.org/10.3390/genes12030342; Blaszczak et al., 2024, Molecular & Cellular Proteomics, https://doi.org/10.1016/j.mcpro.2023.100695 |
| Localization | The gathered evidence strongly supports Hst3 acting on chromatin-associated nuclear histone substrate H3K56, but the excerpts reviewed here do not provide a direct explicit localization statement for Hst3 protein itself. This contrasts with Hst4, for which one review excerpt notes exclusion from the nucleus during G2/M. Therefore, for Hst3, nuclear/chromatin-localized function is inferred from substrate and pathway context, while explicit localization evidence was not extracted in this run. (gershon2021theamazingacrobat pages 4-5, frigerio2023thechromatinlandscape pages 23-24, delgoshaie2013studyofhistone pages 44-48) | Gershon & Kupiec, 2021, Genes, https://doi.org/10.3390/genes12030342; Frigerio et al., 2023, International Journal of Molecular Sciences, https://doi.org/10.3390/ijms24043248 |
| Recent developments (2023โ2024) | Recent literature in this evidence set does not redefine core Hst3 biochemistry but extends its systems-level context: a 2023 review emphasizes Hst3/Hst4 in DSB-repair-associated chromatin dynamics and checkpoint control; a 2023 transcription review links Hst3โRNA exosome function to mRNA/transcription homeostasis; and a 2024 proteome-wide study confirms rapid MMS-triggered Hst3 turnover, shows stabilization when nuclear proteasome function is blocked, and notes that HST3 overexpression compromises growth in MMS. (frigerio2023thechromatinlandscape pages 23-24, bryll2023thecircularlogic pages 8-9, blaszczak2024dissectingubiquitylationand pages 7-9) | Frigerio et al., 2023, International Journal of Molecular Sciences, https://doi.org/10.3390/ijms24043248; Bryll & Peterson, 2023, Transcription, https://doi.org/10.1080/21541264.2023.2183684; Blaszczak et al., 2024, Molecular & Cellular Proteomics, https://doi.org/10.1016/j.mcpro.2023.100695 |
Table: This table summarizes identity, enzymatic function, substrate specificity, regulation, phenotypes, and recent literature for Saccharomyces cerevisiae HST3 using only evidence gathered in this run. It is useful as a compact, citation-backed functional annotation artifact for downstream report writing.
This run did not retrieve a primary localization experiment explicitly stating Hst3โs subcellular localization; nuclear/chromatin action is inferred from substrate and pathway context within the extracted text (gershon2021theamazingacrobat pages 4-5). Additionally, no 2023โ2024 primary paper in this run directly provided new biochemical kinetics for Hst3; recent papers primarily provide systems-level DDR/proteostasis context (blaszczak2024dissectingubiquitylationand pages 7-9, frigerio2023thechromatinlandscape pages 23-24).
References
(maas2006cellcycleand pages 8-9): Nancy L. Maas, Kyle M. Miller, Lisa G. DeFazio, and David P. Toczyski. Cell cycle and checkpoint regulation of histone h3 k56 acetylation by hst3 and hst4. Molecular cell, 23 1:109-19, Jul 2006. URL: https://doi.org/10.1016/j.molcel.2006.06.006, doi:10.1016/j.molcel.2006.06.006. This article has 307 citations and is from a highest quality peer-reviewed journal.
(maas2006cellcycleand pages 2-3): Nancy L. Maas, Kyle M. Miller, Lisa G. DeFazio, and David P. Toczyski. Cell cycle and checkpoint regulation of histone h3 k56 acetylation by hst3 and hst4. Molecular cell, 23 1:109-19, Jul 2006. URL: https://doi.org/10.1016/j.molcel.2006.06.006, doi:10.1016/j.molcel.2006.06.006. This article has 307 citations and is from a highest quality peer-reviewed journal.
(maas2006cellcycleand pages 5-6): Nancy L. Maas, Kyle M. Miller, Lisa G. DeFazio, and David P. Toczyski. Cell cycle and checkpoint regulation of histone h3 k56 acetylation by hst3 and hst4. Molecular cell, 23 1:109-19, Jul 2006. URL: https://doi.org/10.1016/j.molcel.2006.06.006, doi:10.1016/j.molcel.2006.06.006. This article has 307 citations and is from a highest quality peer-reviewed journal.
(delgoshaie2013studyofhistone pages 39-44): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
(maas2006cellcycleand pages 1-2): Nancy L. Maas, Kyle M. Miller, Lisa G. DeFazio, and David P. Toczyski. Cell cycle and checkpoint regulation of histone h3 k56 acetylation by hst3 and hst4. Molecular cell, 23 1:109-19, Jul 2006. URL: https://doi.org/10.1016/j.molcel.2006.06.006, doi:10.1016/j.molcel.2006.06.006. This article has 307 citations and is from a highest quality peer-reviewed journal.
(gershon2021theamazingacrobat pages 4-5): Lihi Gershon and Martin Kupiec. The amazing acrobat: yeastโs histone h3k56 juggles several important roles while maintaining perfect balance. Genes, 12:342, Feb 2021. URL: https://doi.org/10.3390/genes12030342, doi:10.3390/genes12030342. This article has 14 citations.
(delgoshaie2013studyofhistone pages 51-56): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
(delgoshaie2013studyofhistone pages 79-83): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
(delgoshaie2013studyofhistone pages 75-79): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
(maas2006cellcycleand pages 6-8): Nancy L. Maas, Kyle M. Miller, Lisa G. DeFazio, and David P. Toczyski. Cell cycle and checkpoint regulation of histone h3 k56 acetylation by hst3 and hst4. Molecular cell, 23 1:109-19, Jul 2006. URL: https://doi.org/10.1016/j.molcel.2006.06.006, doi:10.1016/j.molcel.2006.06.006. This article has 307 citations and is from a highest quality peer-reviewed journal.
(frigerio2023thechromatinlandscape pages 23-24): Chiara Frigerio, Elena Di Nisio, Michela Galli, Chiara Vittoria Colombo, Rodolfo Negri, and Michela Clerici. The chromatin landscape around dna double-strand breaks in yeast and its influence on dna repair pathway choice. International Journal of Molecular Sciences, 24:3248, Feb 2023. URL: https://doi.org/10.3390/ijms24043248, doi:10.3390/ijms24043248. This article has 32 citations.
(bryll2023thecircularlogic pages 8-9): Alysia R. Bryll and Craig L. Peterson. The circular logic of mrna homeostasis. Transcription, 14:18-26, Feb 2023. URL: https://doi.org/10.1080/21541264.2023.2183684, doi:10.1080/21541264.2023.2183684. This article has 14 citations and is from a peer-reviewed journal.
(blaszczak2024dissectingubiquitylationand pages 7-9): Ewa Blaszczak, Emeline Pasquier, Gaรซlle Le Dez, Adrian Odrzywolski, Natalia Lazarewicz, Audrey Brossard, Emilia Fornal, Piotr Moskalek, Robert Wysocki, and Gwenaรซl Rabut. Dissecting ubiquitylation and dna damage response pathways in the yeast saccharomyces cerevisiae using a proteome-wide approach. Molecular & Cellular Proteomics, 23:100695, Jan 2024. URL: https://doi.org/10.1016/j.mcpro.2023.100695, doi:10.1016/j.mcpro.2023.100695. This article has 3 citations and is from a domain leading peer-reviewed journal.
(delgoshaie2013studyofhistone pages 44-48): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
(delgoshaie2013studyofhistone pages 113-118): N Delgoshaie. Study of histone h3 lysine 56 deacetylation in saccharomyces cerevisiae. Unknown journal, 2013.
id: P53687
gene_symbol: HST3
aliases:
- YOR025W
- OR26.15
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:559292
label: Saccharomyces cerevisiae
description: 'NAD-dependent histone deacetylase HST3, a member of the sirtuin family.
Catalyzes deacetylation of histone H3 lysine 56 (H3K56), a critical residue in nucleosome
assembly during DNA replication and repair. Functions redundantly with HST4 in regulating
transcription, sister chromatid recombination, DNA damage checkpoint control, and
genome stability.'
core_functions:
- molecular_function:
id: GO:0140765
label: histone H3K56 deacetylase activity, NAD-dependent
description: 'NAD-dependent deacetylation of histone H3 lysine 56, catalyzed during
S/G2 phase transition. Essential NAD-dependent H3K56 deacetylase required
for cell cycle checkpoint control and proper nucleosome reassembly after DNA
replication.'
directly_involved_in:
- id: GO:0045892
label: negative regulation of DNA-templated transcription
- id: GO:1990414
label: replication-born double-strand break repair via sister chromatid
exchange
locations:
- id: GO:0005634
label: nucleus
supported_by:
- reference_id: PMID:17977840
supporting_text: Hst3 has NAD-dependent histone deacetylase activity in vitro and that it functions during S phase to deacetylate the core domain of histone H3 at lysine 56 (H3K56)
- reference_id: file:yeast/HST3/HST3-deep-research-falcon.md
supporting_text: Falcon literature synthesis supports HST3 as an NAD-dependent H3K56 deacetylase tied to transcription and genome stability.
- reference_id: file:interpro/panther/PTHR11085/PTHR11085-metadata.yaml
supporting_text: PANTHER PTHR11085 identifies HST3 in the NAD-dependent sirtuin protein deacylase family.
existing_annotations:
- term:
id: GO:0005634
label: nucleus
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'HST3 localizes to the nucleus where it functions as a histone deacetylase.
UniProt subcellular localization states both cytoplasm and nucleus. This IBA
annotation is supported by phylogenetic inference from orthologs. IC evidence
from PMID:12242223 also confirms nuclear localization, which is essential
for its function in histone deacetylation and transcriptional regulation.'
action: ACCEPT
reason: 'HST3 is a nuclear protein required for histone H3K56 deacetylation
during S/G2 phase transitions (PMID:17977840). IBA annotation is well-supported
by orthologous relationships across sirtuins and confirmed experimentally.'
supported_by:
- reference_id: PMID:12242223
supporting_text: 'Furthermore, Hst3 was physically present at 2mu ARS in
a silencing context as well as at the endogenous 2mu plasmid'
- term:
id: GO:0017136
label: histone deacetylase activity, NAD-dependent
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'This parent term captures the correct NAD-dependent histone deacetylase
chemistry, but HST3s core characterized activity is the more specific H3K56
deacetylase activity. Multiple experimental lines of evidence support the
H3K56 substrate specificity.'
action: MODIFY
reason: 'The annotation should use the current specific child term for HST3s
demonstrated NAD-dependent histone H3K56 deacetylase activity.'
proposed_replacement_terms:
- id: GO:0140765
label: histone H3K56 deacetylase activity, NAD-dependent
supported_by:
- reference_id: PMID:17977840
supporting_text: 'Hst3 has NAD-dependent histone deacetylase activity in
vitro and that it functions during S phase to deacetylate the core domain
of histone H3 at lysine 56 (H3K56)'
- reference_id: file:yeast/HST3/HST3-deep-research-falcon.md
supporting_text: Falcon literature synthesis supports HST3 as an NAD-dependent H3K56 deacetylase.
- reference_id: PMID:23357952
supporting_text: 'These functions are necessary for the repair of replication-born
DSBs by SCR'
- term:
id: GO:0000183
label: rDNA heterochromatin formation
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'HST3 contributes to rDNA heterochromatin formation through its NAD-dependent
histone deacetylase activity. However, this term appears somewhat over-specific
compared to the broader silencing roles. UniProt documents roles in histone
H3K56 deacetylation and telomeric silencing. The rDNA-specific annotation
is less well-established than general transcriptional silencing.'
action: KEEP_AS_NON_CORE
reason: 'While HST3 participates in silencing processes that may include rDNA,
this is not explicitly demonstrated as a core function. The primary characterized
substrate is histone H3K56, which affects broader transcription and genome
stability. The rDNA-specific function is an inferred application of the deacetylase
activity rather than a primary function.'
additional_reference_ids:
- PMID:7498786
- PMID:31167142
supported_by:
- reference_id: PMID:7498786
supporting_text: The SIR2 gene family, conserved from bacteria to
humans, functions in silencing, cell cycle progression, and
chromosome stability.
- reference_id: PMID:31167142
supporting_text: Yeast Sirtuin Family Members Maintain Transcription
Homeostasis to Ensure Genome Stability.
- term:
id: GO:0000781
label: chromosome, telomeric region
evidence_type: IEA
original_reference_id: GO_REF:0000108
review:
summary: 'This is a localization annotation indicating HST3 associates with
telomeric regions of chromosomes. Evidence shows HST3 and HST4 contribute
to telomeric silencing (PMID:7498786), but this is inferred primarily from
functional effects rather than direct localization studies. The IEA inference
from GO:0031509 (subtelomeric heterochromatin formation) is logically sound.'
action: KEEP_AS_NON_CORE
reason: 'HST3 function at telomeric regions is secondary to its core H3K56 deacetylase
activity. The localization annotation is supported by functional genomics
(silencing phenotypes) but this is not a primary function description. Better
captured under heterochromatin formation processes.'
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: 'Duplicate of annotation 1 (same GO term, different evidence code).
UniProtKB subcellular location vocabulary explicitly states HST3 is localized
to nucleus and cytoplasm. This IEA annotation from UniProt is consistent with
the IBA annotation.'
action: ACCEPT
reason: 'Redundant but valid annotation. Multiple evidence types (IEA from subcellular
location mapping and IBA from phylogenetics) support nuclear localization.'
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: 'UniProtKB subcellular location states "Cytoplasm. Nucleus." HST3 is
documented in both compartments, though primary function is nuclear. Cytoplasmic
localization is less characterized but appears to be a minor component of
HST3 localization.'
action: KEEP_AS_NON_CORE
reason: 'HST3 has documented cytoplasmic localization in UniProt, but its characterized
functions (H3K56 deacetylation, transcription regulation, DNA repair) are
nuclear. Cytoplasmic localization may represent transit or peripheral functions.'
- term:
id: GO:0006351
label: DNA-templated transcription
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'HST3 involvement in transcription is experimentally confirmed. PMID:31167142
demonstrates that Hst3 and Hst4 regulate transcription homeostasis by repressing
nascent RNA transcription at many loci. This prevents excessive transcription-associated
R-loops that cause DNA damage. The function is broader than suggested by general
"DNA-templated transcription" term.'
action: MODIFY
reason: 'HST3 is documented as repressing transcription through H3K56 deacetylation.
IEA from UniProt keywords (Transcription) is supported by experimental evidence
(PMID:31167142 shows HST3 and HST4 repress nascent transcription), but the
more informative GO term is negative regulation of DNA-templated transcription.'
proposed_replacement_terms:
- id: GO:0045892
label: negative regulation of DNA-templated transcription
supported_by:
- reference_id: PMID:31167142
supporting_text: 'Hst3 and Hst4 are required to repress transcription of
coding and non-coding RNAs'
- term:
id: GO:0016740
label: transferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'Transferase activity is an extremely broad parent term, but it is not
mechanistically wrong for class III/NAD-dependent deacetylases: the acetyl
group is transferred to NAD during the sirtuin reaction. It is much less
informative than the H3K56-specific deacetylase term.'
action: KEEP_AS_NON_CORE
reason: 'GO:0016740 is a valid broad superclass for NAD-dependent deacetylase
chemistry, but HST3s core molecular function is better captured by GO:0140765
histone H3K56 deacetylase activity, NAD-dependent.'
- term:
id: GO:0017136
label: histone deacetylase activity, NAD-dependent
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: 'Duplicate parent-term annotation for NAD-dependent histone deacetylase
activity. The biology is valid, but the stronger HST3-specific review should
point to H3K56 deacetylase activity.'
action: MODIFY
reason: 'Use the specific child term GO:0140765 for HST3s demonstrated H3K56
deacetylase activity.'
proposed_replacement_terms:
- id: GO:0140765
label: histone H3K56 deacetylase activity, NAD-dependent
- term:
id: GO:0031507
label: heterochromatin formation
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: 'HST3 contributes to heterochromatin formation through histone deacetylation.
PMID:7498786 shows hst3 hst4 double mutants are defective in telomeric silencing.
However, PMID:31167142 suggests the primary mechanism is regulation of transcription
homeostasis rather than structural heterochromatin formation. The term is
somewhat over-general for the more specific H3K56 deacetylation function.'
action: KEEP_AS_NON_CORE
reason: 'While HST3 participates in silencing and heterochromatin-associated
processes, its primary characterized function is H3K56 deacetylation and transcription
regulation. Heterochromatin formation is an inferred downstream consequence
rather than direct function.'
- term:
id: GO:0034979
label: NAD-dependent protein lysine deacetylase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: 'This is a correct but broad parent term for NAD-dependent protein lysine
deacetylase chemistry. HST3s characterized substrate is histone H3 lysine 56,
so the parent term should not be promoted as the core MF.'
action: KEEP_AS_NON_CORE
reason: 'The annotation is not wrong, but GO:0140765 is the informative core
molecular-function term for HST3.'
- term:
id: GO:0046872
label: metal ion binding
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'HST3 contains zinc-binding sites. UniProt specifically documents that
HST3 binds 1 zinc ion per subunit, with 4 zinc-coordinating residues in the
catalytic sirtuin domain (positions 195, 198, 220, 223). The annotation is
inferred from UniProt keyword "Zinc" (GO_REF:0000043 is UniProt-KW mapping).
PMID:30358795 on yeast zinc proteome may provide additional validation.'
action: ACCEPT
reason: 'HST3 contains a zinc cofactor essential for sirtuin catalytic activity.
The annotation is well-supported by UniProt feature annotations identifying
zinc-binding residues.'
- term:
id: GO:0070403
label: NAD+ binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: 'HST3 is an NAD-dependent deacetylase and must bind NAD+ cofactor.
UniProt documents multiple NAD+-binding residues (positions 60-79, 151-154,
282-284, 312-314, 333) in the characteristic sirtuin NAD+ binding domain.
The inference from InterPro IPR003000 (sirtuin domain) is appropriate. This
is a required cofactor binding activity.'
action: ACCEPT
reason: 'Essential cofactor binding for catalytic activity. HST3 catalytic mechanism
absolutely requires NAD+ binding. The annotation is correctly inferred from
the sirtuin domain structure.'
- term:
id: GO:0008270
label: zinc ion binding
evidence_type: RCA
original_reference_id: PMID:30358795
review:
summary: 'Zinc ion binding is specifically documented by UniProt with four coordinating
residues identified through structure. RCA (Reviewed Computational Analysis)
using PMID:30358795 (yeast zinc proteome characterization) is appropriate
evidence. This is equivalent to the metal ion binding annotation but more
specific.'
action: ACCEPT
reason: 'Specific instance of the broader metal ion binding annotation. Zinc
is specifically required for sirtuin catalytic activity. RCA evidence from
zinc proteome characterization is valid.'
supported_by:
- reference_id: PMID:30358795
supporting_text: The cellular economy of the Saccharomyces cerevisiae
zinc proteome.
- term:
id: GO:0005634
label: nucleus
evidence_type: IC
original_reference_id: PMID:12242223
review:
summary: 'Third annotation of nuclear localization. PMID:12242223 provides experimental
evidence that HST3 is physically present at the 2mu ARS silencer element in
a silencing context, inferred curated evidence (IC) of nuclear localization.
Redundant with annotations 1 and 5.'
action: ACCEPT
reason: 'Valid experimental evidence of nuclear localization through physical
presence at genomic elements. Redundant with other nuclear localization annotations
but valid.'
supported_by:
- reference_id: PMID:12242223
supporting_text: 'Furthermore, Hst3 was physically present at 2mu ARS in
a silencing context as well as at the endogenous 2mu plasmid'
- term:
id: GO:0031509
label: subtelomeric heterochromatin formation
evidence_type: IGI
original_reference_id: PMID:7498786
review:
summary: 'PMID:7498786 shows that hst3 hst4 double mutants are defective in
telomeric silencing, establishing that HST3 and HST4 contribute together to
subtelomeric silencing. IGI (Inferred from Genetic Interaction) is appropriate
evidence code, using HST4 as the interacting gene. This demonstrates HST3
function in telomeric silencing.'
action: ACCEPT
reason: 'Experimental evidence demonstrates HST3 requirement for subtelomeric
silencing. The function is well-characterized even if redundant with HST4.
This is a core genomic stability function.'
supported_by:
- reference_id: PMID:7498786
supporting_text: 'hst3 hst4 double mutants are defective in telomeric silencing'
- term:
id: GO:0017136
label: histone deacetylase activity, NAD-dependent
evidence_type: IDA
original_reference_id: PMID:17977840
review:
summary: 'IDA evidence from PMID:17977840 directly supports the specific H3K56
NAD-dependent deacetylase activity, not just the parent histone deacetylase
term.'
action: MODIFY
reason: 'The direct assay evidence should be represented with GO:0140765, the
specific H3K56 child term.'
proposed_replacement_terms:
- id: GO:0140765
label: histone H3K56 deacetylase activity, NAD-dependent
supported_by:
- reference_id: PMID:17977840
supporting_text: 'Hst3 has NAD-dependent histone deacetylase activity in
vitro and that it functions during S phase to deacetylate the core domain
of histone H3 at lysine 56 (H3K56)'
- term:
id: GO:0017136
label: histone deacetylase activity, NAD-dependent
evidence_type: IMP
original_reference_id: PMID:17977840
review:
summary: 'IMP evidence from PMID:17977840 supports the specific H3K56 deacetylase
function: loss of Hst3 causes failure to regulate H3K56 acetylation and downstream
checkpoint/cohesion phenotypes.'
action: MODIFY
reason: 'The mutant phenotype evidence should be represented with GO:0140765
rather than only the parent NAD-dependent histone deacetylase term.'
proposed_replacement_terms:
- id: GO:0140765
label: histone H3K56 deacetylase activity, NAD-dependent
supported_by:
- reference_id: PMID:17977840
supporting_text: 'Loss of Hst3-mediated regulation of H3K56 acetylation
results in a defect in the S phase DNA damage checkpoint'
- term:
id: GO:0006351
label: DNA-templated transcription
evidence_type: IDA
original_reference_id: PMID:31167142
review:
summary: 'IDA evidence from PMID:31167142 shows comprehensive transcriptomic
analysis demonstrating HST3 directly regulates transcription. Using NET-seq
(native elongating transcript sequencing), the authors show that loss of Hst3
and Hst4 leads to global increases in nascent transcription at ~1,000 genes.
This is direct measurement of transcription dynamics, not merely inference.
Highly specific to H3K56-mediated regulation.'
action: MODIFY
reason: 'Robust experimental evidence supports transcriptional repression:
NET-seq shows increased nascent transcription when HST3/HST4 are lost. The
parent DNA-templated transcription term should be replaced by the more precise
negative regulation term.'
proposed_replacement_terms:
- id: GO:0045892
label: negative regulation of DNA-templated transcription
supported_by:
- reference_id: PMID:31167142
supporting_text: 'Loss of Hst3 and Hst4 led to a global shift in the nascent
RNA transcriptome, with an average fold increase of ~1.4'
- term:
id: GO:0009299
label: mRNA transcription
evidence_type: IDA
original_reference_id: PMID:31167142
review:
summary: 'PMID:31167142 demonstrates that HST3 negatively regulates RNA
polymerase II mRNA transcription: metagene analysis shows higher nascent
transcript levels throughout genic regions, especially near transcription
start sites, when HST3/HST4 activity is lost.'
action: MODIFY
reason: 'Direct NET-seq evidence shows mRNA-coding regions are specifically
affected, but the direction is repressive rather than neutral participation
in mRNA transcription. The annotation should therefore use a negative
regulation child term consistent with the GO:0006351 reviews from the same
paper.'
proposed_replacement_terms:
- id: GO:0000122
label: negative regulation of transcription by RNA polymerase II
supported_by:
- reference_id: PMID:31167142
supporting_text: 'Metagene plots of mean nascent transcript levels, representative
genome browser views of NET-seq data, and a heatmap of the log2-fold change
between the hst4ฮ HST3-FRB mutant and WT confirmed higher levels of transcription
throughout genic regions'
- term:
id: GO:1990414
label: replication-born double-strand break repair via sister chromatid
exchange
evidence_type: IMP
original_reference_id: PMID:23357952
review:
summary: 'PMID:23357952 provides comprehensive evidence that HST3 is required
for sister chromatid recombination (SCR) of replication-born double-strand
breaks. The authors identify hst3 among 12 mutants consistently impaired in
SCR using physical assay of recombination. Loss of HST3 (and HST4) severely
impairs the ability to repair DSBs with the sister chromatid, with 50-fold
decrease in intrachromosomal SCR. This is a major genome stability function
dependent on H3K56 acetylation state.'
action: ACCEPT
reason: 'HST3 is a critical factor for proper DSB repair template choice (sister
chromatid preference). Loss results in genome instability and increased recombination
with homologs instead of sister chromatids. Core function in genome stability.'
supported_by:
- reference_id: PMID:23357952
supporting_text: 'The hst3ฮ mutation is strongly affected in intrachromosomal
SCR repeat recombination (50-fold decrease)'
- term:
id: GO:0046459
label: short-chain fatty acid metabolic process
evidence_type: IMP
original_reference_id: PMID:12618394
review:
summary: 'PMID:12618394 shows that growth on short-chain fatty acids (acetate,
propionate) is severely impaired in quintuple sir2 hst1 hst2 hst3 hst4 mutant
strain, with HST3 and HST4 identified as most important for growth on these
substrates. However, this is not the primary function of HST3. The mechanism
appears to involve SIR2 family proteins controlling acetyl-CoA synthetase
(Acs) enzyme activity, suggesting an indirect metabolic role rather than direct
involvement in lipid metabolism.'
action: MARK_AS_OVER_ANNOTATED
reason: 'While HST3 contributes to growth on short-chain fatty acids through
its requirement for Acs activity regulation, this is not a primary enzymatic
function. HST3 is a histone deacetylase whose role in fatty acid metabolism
is indirect, mediated through NAD-dependent regulation of Acs protein acetylation.
The annotation overstates HST3s direct involvement in metabolic process. Better
annotated as a regulatory cofactor effect than a metabolic process function.'
additional_reference_ids:
- PMID:12618394
supported_by:
- reference_id: PMID:12618394
supporting_text: Short-chain fatty acid activation by acyl-coenzyme A
synthetases requires SIR2 protein function in Salmonella enterica
and Saccharomyces cerevisiae.
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with
GO terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword
mapping
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular
Location vocabulary mapping, accompanied by conservative changes to GO
terms applied by UniProt
findings: []
- id: GO_REF:0000108
title: Automatic assignment of GO terms using logical inference, based on on
inter-ontology links
findings: []
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning
models
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:12242223
title: A novel yeast silencer. the 2mu origin of Saccharomyces cerevisiae
has HST3-, MIG1- and SIR-dependent silencing activity.
findings: []
- id: PMID:12618394
title: Short-chain fatty acid activation by acyl-coenzyme A synthetases
requires SIR2 protein function in Salmonella enterica and Saccharomyces
cerevisiae.
findings: []
- id: PMID:17977840
title: Hst3 is regulated by Mec1-dependent proteolysis and controls the S
phase checkpoint and sister chromatid cohesion by deacetylating histone H3
at lysine 56.
findings: []
- id: PMID:23357952
title: Histone H3K56 acetylation, Rad52, and non-DNA repair factors control
double-strand break repair choice with the sister chromatid.
findings: []
- id: PMID:30358795
title: The cellular economy of the Saccharomyces cerevisiae zinc proteome.
findings: []
- id: PMID:31167142
title: Yeast Sirtuin Family Members Maintain Transcription Homeostasis to
Ensure Genome Stability.
findings: []
- id: PMID:7498786
title: The SIR2 gene family, conserved from bacteria to humans, functions in
silencing, cell cycle progression, and chromosome stability.
findings: []
- id: file:yeast/HST3/HST3-deep-research-falcon.md
title: Falcon deep research synthesis for HST3
findings: []
- id: file:interpro/panther/PTHR11085/PTHR11085-metadata.yaml
title: PANTHER family PTHR11085 NAD-dependent sirtuin protein deacylase metadata
findings: []