| Functional facet | Summary | Key domains / inferred activity | Major partners | Key evidence | Representative recent sources |
|---|---|---|---|---|---|
| Identity / verification | **UniProt O94267** matches **Schizosaccharomyces pombe spt16+**, the essential large subunit of the conserved **FACT** histone-chaperone complex; in fission yeast FACT is built from an **Spt16/Pob3 heterodimer** plus the HMGB protein **Nhp6**. This matches the user-provided protein description and excludes confusion with unrelated genes. (pqac-00000013, pqac-00000014, pqac-00000016) | Conserved Spt16 architecture in yeast FACT; essential chromatin factor rather than enzyme with a small-molecule substrate. (pqac-00000013, pqac-00000015) | Pob3, Nhp6 | “Spt16/Pob3 heterodimer”; “spt16+ is essential”; “Nhp6 accessory HMGB module”. (pqac-00000013, pqac-00000016) | Takahata & Murakami, **Feb 2023**, Biomolecules, DOI: https://doi.org/10.3390/biom13020377; Takahata et al., **Jun 2024**, Genes to Cells, DOI: https://doi.org/10.1111/gtc.13132 |
| Domain architecture | Recent fission-yeast literature depicts Spt16/FACT with a **peptidase-like N-terminal fold**, **dimerization domain**, **tandem PH domains**, and **acidic tail(s)**; these align well with UniProt/InterPro annotations for O94267. (pqac-00000013, pqac-00000014, pqac-00000018) | **Peptidase-like/peptidase M24-like fold**: H3/H4 binding and protein interactions; **tandem PH domain(s)**: H2A/H2B chaperone function; **acidic tail**: H2A/H2B tethering, DNA-mimic-like behavior; **DD**: Spt16-Pob3 assembly. (pqac-00000013, pqac-00000015, pqac-00000018) | Pob3, core histones | “PL domain”; “PH1/PH2”; “acidic cluster”; “C-terminal acidic tail required for H2A/H2B binding”. (pqac-00000013, pqac-00000018) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377; Takahata et al., **Jun 2024**, https://doi.org/10.1111/gtc.13132 |
| Core molecular function | Spt16 is best understood as a **histone chaperone/chromatin transaction factor**, not a peptidase enzyme: it promotes nucleosome reorganization, especially **H2A-H2B dimer handling** and stabilization of partially disrupted nucleosomes during transcription and replication. (pqac-00000013, pqac-00000015) | H3/H4 engagement via N-terminal peptidase-like region; H2A/H2B deposition/removal via PH and acidic regions; ATP-independent chromatin remodeling support. (pqac-00000013, pqac-00000015) | Histones H3/H4 and H2A/H2B | “histone H2A/H2B chaperone”; “displace H2A/H2B dimers”; “preserve nucleosome integrity”. (pqac-00000013, pqac-00000015) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377; Jang et al., preprint posted **Jun 2024**, later NAR, https://doi.org/10.1101/2024.06.17.599424 |
| Euchromatin / transcription role | In euchromatin, FACT/Spt16 supports **transcription elongation** by helping RNA polymerase traverse chromatin while maintaining nucleosome integrity; pob3Δ and spt4Δ show correlated transcriptional defects, whereas nhp6Δ is much milder, implying the Spt16/Pob3 core is the main transcriptional module. (pqac-00000002, pqac-00000006) | Nucleosome engagement and H2A/H2B exchange/repositioning during elongation. (pqac-00000013, pqac-00000006) | Pob3, Spt5/DSIF, RNAP-associated chromatin | “FACT functions as a transcription elongation factor”; “pob3Δ and spt4Δ transcriptomes correlated”; “Spt16/Pob3 interacts with Spt5”. (pqac-00000002, pqac-00000006) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377; Takahata et al., **Jun 2024**, https://doi.org/10.1111/gtc.13132 |
| Heterochromatin role | In fission yeast heterochromatin, Spt16 has a prominent **silencing and chromatin-condensation** role: FACT is recruited to H3K9me/Swi6 chromatin, suppresses histone turnover, promotes proper H2A/H2B maintenance, and supports establishment/maintenance of silenced chromatin. (pqac-00000001, pqac-00000002, pqac-00000017) | Peptidase-like domain recruitment to HP1/Swi6 followed by scaffold shift to histone H3/H4; H2A/H2B repositioning on heterochromatic nucleosomes. (pqac-00000001, pqac-00000009) | Swi6/HP1, Pob3, histones | “FACT strongly suppresses histone turnover”; “critical role in establishment and maintenance of heterochromatin”. (pqac-00000001, pqac-00000017) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377; Takahata et al., **Jun 2024**, https://doi.org/10.1111/gtc.13132 |
| Direct HP1/Swi6 interaction | A key S. pombe-specific finding is that the **peptidase-like domain of Spt16 directly binds the dimerized chromo-shadow domain of Swi6/HP1**, via an unusual interaction dependent on the **RKDD** loop in Swi6; mutating this loop abolishes Spt16 binding and perturbs heterochromatin. (pqac-00000001, pqac-00000009) | Peptidase-like domain acts as a protein-interaction module in addition to histone binding. (pqac-00000001) | Swi6/HP1 | “directly binds dimerized Swi6-CSD”; “Swi6-4A lost Spt16 binding”; “heterochromatin significantly disordered”. (pqac-00000001, pqac-00000009) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377 |
| Pob3 dependence / independence | Pob3 promotes Spt16 recruitment and function, but Spt16 also shows **Pob3-independent activity** in fission yeast. In **pob3Δ**, Spt16 occupancy at heterochromatin falls to about **50% of wild type**, indicating partial dependence but not full loss of recruitment. (pqac-00000000, pqac-00000019) | DD-mediated core FACT assembly; Pob3 tandem PH contributes H3/H4 recognition in some models. (pqac-00000009) | Pob3, Swi6 | “Spt16 binding reduced to ~50% in pob3Δ”; “additive defect in pob3Δ swi6Δ”. (pqac-00000000, pqac-00000019) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377 |
| Nhp6 / HMG-box module | Nhp6 provides an **HMGB DNA-binding/bending module** that enhances FACT chromatin engagement. In 2024 work, Nhp6 alone had minor expression effects, but fusing Nhp6 to Pob3 increased FACT chromatin binding and promoted heterochromatin formation, indicating the HMG module tunes chromatin affinity and epigenetic stability. (pqac-00000005, pqac-00000006, pqac-00000016) | HMGB-mediated DNA binding/bending; promotes FACT opening/nucleosome recognition. (pqac-00000013, pqac-00000016) | Pob3, DNA, nucleosomes | “Pob3-Nhp6 fusion increased chromatin binding”; “promoted heterochromatin”; “Nhp6 mutants had little effect alone”. (pqac-00000005, pqac-00000016) | Takahata et al., **Jun 2024**, https://doi.org/10.1111/gtc.13132; Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377 |
| Replication-coupled chromatin role | Beyond transcription, recent work places FACT/Spt16 at the **replisome**, where it helps retain/recycle parental histones during replication of heterochromatin. FACT associates with replisome components, and models propose it captures released histones and redeposits them on daughter strands to preserve H3K9me inheritance. (pqac-00000012, pqac-00000021) | Histone-chaperone role during S phase; interfaces with replisome-linked histone recycling pathways. (pqac-00000012, pqac-00000020) | Mcl1/Ctf4 ortholog, Mcm2, GINS, Polα, Swi6/HP1 | “FACT association with the replisome”; “help retain parental histones”; “co-IP of FACT (Pob3) with Mcm2/Psf3 depends on Mcl1”. (pqac-00000012, pqac-00000021) | Nathanailidou et al., **Jan 2024**, PNAS, https://doi.org/10.1073/pnas.2315596121 |
| Localization / cellular context | Functionally, Spt16 acts on **nuclear chromatin** in both **transcribed euchromatin** and **H3K9-methylated heterochromatin**, and during S phase it is also linked to **replication forks/replisome-enriched heterochromatin domains**. (pqac-00000002, pqac-00000012) | Chromatin-bound histone chaperone; no evidence here for extracellular or membrane localization. (pqac-00000002, pqac-00000012) | Chromatin, heterochromatin, replisome | “binds heterochromatic regions”; “enriched replisome components together with FACT”; “retains parental histones during DNA replication”. (pqac-00000012, pqac-00000019) | Takahata & Murakami, **Feb 2023**, https://doi.org/10.3390/biom13020377; Nathanailidou et al., **Jan 2024**, https://doi.org/10.1073/pnas.2315596121 |


*Table: This table verifies that UniProt O94267 corresponds to the Schizosaccharomyces pombe FACT subunit Spt16 and summarizes its domain organization, major partners, and experimentally supported roles in transcription, heterochromatin, and replication. It emphasizes recent 2023–2024 literature and short evidence phrases to support each functional facet.*