SIR4

Summary: IEA annotation based on UniProtKB keyword mapping. SIR4 does possess DNA-binding capability, though secondary to its adaptor role.

Reason: SIR4 has demonstrable DNA-binding activity (confirmed by biochemical assays and in vitro reconstitution), but this is not its primary functional role. The protein binds DNA primarily as part of the heterotrimer complex structure and to stabilize chromatin interactions. This is more accurately described by more specific terms like "double-stranded DNA binding" (GO:0003690) or "nucleosome binding" (GO:0031491), both of which are already captured in the annotation set.

Summary: Cellular compartment annotation based on UniProtKB subcellular location mapping.

Reason: SIR4 is definitively a nuclear protein, as established by localization studies and its function in silent chromatin complexes at telomeres and mating-type loci. This is a core cellular location for the protein.

Summary: IEA annotation from UniProtKB keyword mapping. However, SIR4 is not directly involved in the catalytic process of transcription but rather in transcriptional repression.

Reason: This is a poor characterization of SIR4 function. SIR4 is involved in transcriptional silencing/repression through chromatin structure modification, not in the process of DNA-templated transcription itself. DNA-templated transcription (GO:0006351) is too general and misleading, as it includes active transcription, which is the opposite of SIR4s silencing role. This annotation should be removed in favor of the more accurate "heterochromatin formation" (GO:0031507) terms already in the set.

Summary: IPI annotation documenting SIR4 interaction with RAP1. Multiple protein binding annotations reflect SIR4s role in protein-protein interactions within the silencing complex.

Reason: The underlying RAP1 interaction is real, but the generic "protein binding" (GO:0005515) term is uninformative per curation guidelines. The functionally meaningful aspect of this interaction (SIR4 bridging RAP1 to the SIR2/SIR3 machinery) is precisely captured by the accepted GO:0060090 (molecular adaptor activity) annotation, so this generic term is over-annotated and not retained as a core function.

Summary: IPI annotation documenting SIR4 interactions with SIR2, SIR3 and possibly histone proteins from mass spectrometry analysis of protein complexes.

Reason: The SIR2/SIR3 interactions are real, but generic "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s functional role in assembling these partners is captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation documenting SIR4 interaction with YKU80 (Ku80), a component of the non-homologous end-joining machinery.

Reason: The YKU80 interaction is real and biologically relevant to telomere tethering, but generic "protein binding" (GO:0005515) is uninformative per curation guidelines. The functional consequences are captured by GO:0034398 (telomere tethering at nuclear periphery) and GO:0060090 (molecular adaptor activity), so this generic term is over-annotated.

Summary: IPI annotation from biochemical studies of silencing complex composition and protein interactions.

Reason: Generic "protein binding" (GO:0005515) is uninformative per curation guidelines. The relevant SIR complex assembly function is already captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation from proteome survey identifying SIR4 as a component of multiple protein complexes.

Reason: High-throughput proteomic evidence for "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s scaffolding role is captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation from global landscape study of yeast protein complexes, confirming SIR4s involvement in complex assembly.

Reason: High-throughput proteomic "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s role in protein assemblies is captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation from structure-function analysis of SIR3, documenting its interaction with SIR4.

Reason: The SIR3-SIR4 interaction is real, but generic "protein binding" (GO:0005515) is uninformative per curation guidelines. This interaction underlies SIR4s adaptor/scaffold role, captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation documenting SIR4 interaction with SIR2 in context of cohesin-associated factors affecting recombination.

Reason: The SIR2 interaction is real, but generic "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s functional coupling to the SIR2 deacetylase is captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation from histone chaperone studies documenting CAF-1 interactions relevant to silent chromatin assembly.

Reason: Generic "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s contribution to silent chromatin assembly is captured by the heterochromatin formation terms (GO:0031507/GO:0031509) and GO:0060090 (molecular adaptor activity), so this generic term is over-annotated.

Summary: IPI annotation from atlas of chaperone-protein interactions, documenting interactions with histone chaperones.

Reason: High-throughput chaperone-interaction "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s functional role in complex assembly is captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation from budding yeast chromatin-associated interactome defining SIR4 binding partners.

Reason: High-throughput interactome "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s functional interactions are captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: IPI annotation documenting SIR4 interactions with RAP1 and nucleoporin NUP170 from chromatin isolation studies.

Reason: The RAP1/NUP170 interactions are real, but generic "protein binding" (GO:0005515) is uninformative per curation guidelines. The functional connection to nuclear organization is captured by GO:0034398 (telomere tethering at nuclear periphery) and GO:0060090 (molecular adaptor activity), so this generic term is over-annotated.

Summary: IPI annotation from recent social and structural architecture study of the yeast protein interactome.

Reason: High-throughput interactome "protein binding" (GO:0005515) is uninformative per curation guidelines. SIR4s functional interactions are captured by GO:0060090 (molecular adaptor activity) and GO:0005677 (chromatin silencing complex), so this generic term is over-annotated.

Summary: NAS annotation from review of silencing complex function, indicating SIR4 involvement in forming and maintaining heterochromatin.

Reason: This is a core functional annotation for SIR4. The protein is essential for heterochromatin formation at multiple loci. SIR4 participates in the structural assembly of silent chromatin through its role as a scaffolding protein.

Summary: IMP annotation from early position effect studies using classical yeast genetics, demonstrating that SIR4 is required for silencing genes near telomeres.

Reason: This is a core and well-established function of SIR4. Genetic studies definitively show SIR4 mutants lose subtelomeric silencing. This is a primary functional role.

Summary: IMP annotation from detailed mutational analysis of SIR4 N-terminus showing its role in linker DNA protection and subtelomeric silencing.

Reason: Demonstrates through site-specific mutations that SIR4s DNA-binding N-terminal domain is critical for maintaining subtelomeric heterochromatin.

Summary: IMP annotation from analysis linking Ku-dependent DNA repair to telomeric silencing, demonstrating SIR4s role in both processes.

Reason: Establishes that SIR4 is essential for telomeric heterochromatin formation and also participates in DNA repair at telomeres.

Summary: IMP annotation from quiescence-associated study showing SIR4 is required for telomere organization at the nuclear periphery.

Reason: This is an appropriate cellular component annotation, indicating SIR4 localizes to and functions at telomeric regions. The functional involvement (IMP evidence) shows SIR4 is required for proper telomere organization.

Summary: IDA annotation from binding studies showing SIR4 protein physically binds telomeric DNA in vivo.

Reason: Direct biochemical evidence of SIR4 localization to telomeres, confirmed by chromatin immunoprecipitation and related assays.

Summary: IMP annotation from recent study of heterochromatin assembly showing SIR4 abundance regulates formation of silent chromatin at multiple loci.

Reason: Demonstrates that SIR4 protein levels directly control the extent of heterochromatin formation, confirming its central role in assembly of silent chromatin.

Summary: IMP annotation showing SIR4 is required for silencing at HML and HMR mating-type loci.

Reason: This is a core function of SIR4. The silencing of mating-type loci (HML, HMR) by the SIR complex is a classic and essential yeast function, and SIR4 is required for this process.

Summary: IMP annotation from genetic studies showing SIR4 mediates the interaction between telomeric binding factor RAP1 and the rest of the silencing machinery.

Reason: This is a precise characterization of SIR4s molecular function. SIR4 acts as a critical adaptor protein, bridging the DNA-binding factor RAP1 to the SIR2/SIR3 silencing enzymes. This is a core and well-established function.

Summary: IMP annotation from study of telomerase recruitment, showing SIR4 is involved in bringing protein complexes to telomeres.

Reason: SIR4 plays a role in recruiting the SIR complex to telomeres, which is accurately described by this specific term capturing both the complex assembly and localization aspects.

Summary: IDA annotation from biophysical studies demonstrating SIR4 directly binds double-stranded DNA in vitro through its N-terminal domain.

Reason: SIR4 has demonstrated DNA-binding activity, specifically for double-stranded DNA. This is more specific than the general "DNA binding" term and is appropriate for a core function.

Summary: IMP annotation showing that SIR4s DNA-binding function is required for silencing, not just that it can bind DNA in vitro.

Reason: Functional evidence that SIR4s DNA-binding activity is essential for its biological role. The two annotations (IDA and IMP) together establish both the capability and necessity of this function.

Summary: sir4 mutants are genuinely NHEJ-defective, but the defect is an indirect consequence of losing HML/HMR silencing - derepressed a1/alpha2 shuts off the NHEJ factor NEJ1 - rather than a direct role for SIR4 in end-joining, so a regulation term describes the biology better than the participant term.

Reason: The IMP evidence is real and the cited paper assayed SIR4 directly: "using an in vivo plasmid rejoining assay, we demonstrate that SIR2, SIR3 and SIR4...are essential for Ku-dependent DSB repair" (PMID:9501103), so the previous MARK_AS_OVER_ANNOTATED mischaracterised a directly demonstrated genetic requirement as likely spurious. The mechanism, however, is indirect, and that determines the correct term. Lee et al. found that "the effect of deleting SIR genes is largely attributable to derepression of silent mating-type genes" (PMID:10421582), and Kegel et al. identified the target: NEJ1 is haploid-specific, its promoter carries a consensus a1/alpha2 repressor site, and its transcription is completely repressed in sir haploids - so loss of SIR silencing lets a1/alpha2 shut NEJ1 off (PMID:11676923). Decisively, constitutive Nej1p expression "completely rescued the defect in NHEJ, thus showing that Sir proteins per se were dispensable for NHEJ" (PMID:11676923) - an experiment whose sir mutant panel explicitly included Sir4p. SIR4 is thus not part of the core NHEJ machinery (Ku70/80, Lig4/Dnl4, Xrs2) and, on the rescue evidence, is not a participant in end-joining at all; it acts upstream by silencing HML/HMR so that NEJ1 stays expressed. (Lee et al. do report a residual "minor role" for Sir proteins in end-joining, but the Kegel rescue shows it is not required.) The general regulation term GO:2001032 is proposed rather than the directional GO:2001034 because SIR4 acts permissively - maintaining NEJ1 expression - rather than actively modulating repair. This adjudication is deliberately identical to the one merged for SIR3 (PR #2944) on the same annotation, evidence code and reference, since a single experiment assayed all three Sir proteins; SIR2 still carries REMOVE for this annotation and should be reconciled in the same way.

Proposed replacements: regulation of double-strand break repair via nonhomologous end joining

Summary: IMP annotation from mutational studies showing SIR4 N-terminus is required for silencing at HML/HMR loci.

Reason: Demonstrates through structure-function analysis that SIR4 N-terminal domain is specifically required for mating-type locus silencing.

Summary: IGI annotation showing genetic interaction between SIR4 and another silencing component in maintaining HML/HMR heterochromatin.

Reason: Genetic interaction evidence confirming SIR4s functional involvement in mating-type silencing through interaction with other silencing genes.

Summary: IMP annotation from seminal position effect studies identifying SIR4 as required for mating-type locus silencing.

Reason: Early classical genetic evidence establishing SIR4 as an essential component of the silencing system at HML and HMR.

Summary: IMP annotation showing SIR4 promotes formation of silent chromatin, not just participates as a structural component.

Reason: Demonstrates that SIR4 abundance positively regulates the extent of heterochromatin formation across the genome. This captures its regulatory role beyond just being present in the complex.

Summary: IMP annotation from cell biology study showing SIR4 is required for telomeres to cluster at the nuclear periphery during quiescence.

Reason: This is an important functional role of SIR4 linking chromatin silencing to nuclear organization. SIR4 interacts with nuclear pore and nuclear envelope proteins (MPS3, NUP170) to position telomeres at the nuclear margin.

Summary: IMP annotation from another study confirming SIR4 is required for telomere organization at the nuclear envelope.

Reason: Additional evidence establishing SIR4s role in telomere positioning through interaction with nuclear structural components.

Summary: IDA annotation from biochemical reconstitution showing SIR4 within the SIR2-3-4 heterotrimer binds double-stranded DNA with strong nonspecific activity.

Reason: In vitro biochemical evidence for SIR4 DNA-binding capability in the context of the native silencing complex.

Summary: IDA annotation showing SIR4 is a component of the chromatin silencing complex through biochemical purification and characterization.

Reason: This is a core cellular component annotation establishing SIR4 as a structural member of the SIR2-SIR3-SIR4 silent chromatin complex.

Summary: IDA annotation from biochemical reconstitution showing SIR4 within the SIR2-SIR3-SIR4 complex binds to nucleosomes.

Reason: SIR4 directly contacts nucleosomes as part of the silencing complex assembly and maintenance of silent chromatin structure. This is a core function.