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histone-fold domain found in protein SPT3 and similar proteins SPT3, also called suppressor of Ty 3 homolog, or positive regulator of Ty transcription, is a component of the transcription regulatory histone acetylation (HAT) complexes SAGA, SALSA and SLIK. SAGA (Spt-Ada-Gcn5-acetyltransferase) is involved in RNA polymerase II-dependent transcriptional regulation of approximately 10% of yeast genes. At the promoters, SAGA is required for recruitment of the basal transcription machinery. It influences RNA polymerase II transcriptional activity through different activities such as TATA binding protein (TBP) interaction (SPT3, SPT8 and SPT20) and promoter selectivity, interaction with transcription activators (GCN5, ADA2, ADA3 and TRA1), and chromatin modification through histone acetylation (GCN5) and deubiquitination (UBP8). SAGA acetylates nucleosomal histone H3 to some extent (to form H3K9ac, H3K14ac, H3K18ac and H3K23ac). SAGA interacts with DNA via upstream activating sequences (UASs). SALSA (SAGA altered, SPT8 absent), an altered form of SAGA, may be involved in positive transcriptional regulation. Besides lacking SPT8, SALSA contains an SPT7 subunit that is truncated. SPT3 is required for recruitment of TATA-binding protein (TBP) to SAGA-dependent promoters. During SAGA-mediated transcriptional inhibition, SPT3 and SPT8 prevent binding of TBP to the TATA box. SLIK (SAGA-like) is proposed to have partly overlapping functions with SAGA. It preferentially acetylates methylated histone H3, at least after activation at the GAL1-10 locus. SPT factors 3, 7 and 8 are required for the initiation of Ty transcription from the delta promoter. SPT3 regulates Ty1 as well as mating factor genes. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",