SUPT7L

SUPT7L (STAF65gamma) is a structural scaffolding subunit of the STAGA/SAGA histone acetyltransferase coactivator complex that maintains complex integrity by enabling the stable association of TRRAP and GCN5 with the SPT3 and TAF9 modules (PMID:17967894). Through this scaffolding role it governs a defined subset of coactivator recruitment events: SUPT7L is specifically required to bridge SPT3/STAGA to core Mediator and to recruit SPT3, TAF9, and core Mediator to MYC target promoters such as TERT, while being dispensable for MYC recruitment of TRRAP, GCN5, and p300 and for nucleosome acetylation and TFIID/Pol II loading (PMID:17967894). Beyond the canonical coactivator complex, SUPT7L participates in a distinct small TAF complex (SMAT) with TAF8 and TAF10 (PMID:17375202) and acts as a nuclear import chaperone for TAF10, carrying it into the nucleus via its own NLS through an importin-beta-independent mechanism (PMID:15870280). In a separate regulatory mode, SUPT7L functions as a co-repressor, physically associating with YY1 and class IIa HDACs to repress c-Myc in a manner dependent on its SUMOylation, and promoting nuclear enrichment and assembly of class IIa HDAC complexes (PMID:24852358). SUPT7L is required for genome stability: loss of SUPT7L protein increases DNA damage that is normalized by re-expression of wildtype protein (PMID:38592547), consistent with the elevated DNA recombination seen upon deletion of its yeast ortholog Spt7 (PMID:33831401).

1. 2005 High

   Established a non-transcriptional cellular role by showing SUPT7L acts as a dedicated nuclear import chaperone, answering how the TAF10 subunit reaches the nucleus.

   Evidence Fluorescent fusion proteins with NLS mutagenesis, FRAP, and in vitro importin beta binding assays in human cells

   PMID:15870280

   Open questions at the time

   • The importin-beta-independent import mechanism for TAF10 is not molecularly defined
   • Whether SUPT7L chaperones other subunits is untested
2. 2006 Low

   Extended SUPT7L's interaction landscape to TRIP-Br transcriptional regulators, hinting at functions beyond the core coactivator complex.

   Evidence Co-immunoprecipitation and transcriptional reporter assays

   PMID:17141982

   Open questions at the time

   • Single Co-IP without reciprocal or structural validation
   • Functional consequence at native promoters not established
3. 2007 High

   Defined SUPT7L as the structural linchpin of STAGA, answering whether it is a passive subunit or required for complex assembly and which recruitment steps depend on it.

   Evidence siRNA knockdown, reciprocal Co-IP, and ChIP at MYC target promoters in human cells

   PMID:17967894

   Open questions at the time

   • Structural basis for bridging TRRAP/GCN5 to SPT3/TAF9 not resolved
   • Direct binding interfaces within STAGA not mapped
4. 2007 High

   Identified a SUPT7L-containing assembly distinct from TFIID and STAGA (SMAT), showing the protein partitions into multiple complexes.

   Evidence Proteomic identification, Co-IP, and in vitro reconstitution with TAF8 and TAF10

   PMID:17375202

   Open questions at the time

   • Cellular function of SMAT relative to STAGA undefined
   • Stoichiometry and regulation of partitioning between complexes unknown
5. 2014 Medium

   Revealed a repressive, SUMOylation-gated function of SUPT7L, answering whether it acts solely as a coactivator subunit or can also organize repressor complexes.

   Evidence Co-IP, ChIP, SUMOylation assays, and reporter assays examining YY1 and class IIa HDAC association at c-Myc

   PMID:24852358

   Open questions at the time

   • SUMO sites on SUPT7L not mapped
   • How activator versus repressor modes are switched in vivo unclear
6. 2021 Medium

   Used the yeast ortholog to causally link SUPT7L/Spt7-dependent complex integrity to DNA recombination control, framing a genome-stability role.

   Evidence Yeast Spt7 deletion mutants with recombination assays and Rad52 foci imaging in S phase

   PMID:33831401

   Open questions at the time

   • Whether the human protein controls recombination by the same route is not shown
   • Molecular connection between SAGA integrity and recombination undefined
7. 2024 Medium

   Demonstrated in human cells that loss of SUPT7L causes DNA damage rescuable by wildtype re-expression, establishing a direct requirement for genome stability.

   Evidence Patient fibroblasts with biallelic loss-of-function variants, genome-edited HeLa cells, DNA damage assays, and transient overexpression rescue

   PMID:38592547

   Open questions at the time

   • Whether DNA damage arises from transcriptional defects or a direct repair role is unresolved
   • Associated clinical phenotype not mechanistically connected to genome instability
8. 2026 Low

   Placed SUPT7L within a nuclear DARS1–SAGA interaction modulating MYC, expanding the set of factors converging on SUPT7L-associated MYC regulation.

   Evidence Quantitative proteomics, Co-IP, and knockdown with MYC protein/phosphorylation readouts

   PMID:41790991

   Open questions at the time

   • SUPT7L-specific contribution to the DARS1 effect not dissected
   • Direct versus indirect interaction not established

• How SUPT7L's distinct activities — STAGA scaffolding, SMAT/TAF10 chaperoning, HDAC co-repression, and genome stability — are coordinated within a single cell remains unresolved.
• No integrated structural model of SUPT7L across its complexes
• Mechanism coupling SUPT7L loss to DNA damage in humans unknown
• Regulation switching between activator and repressor roles undefined