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Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8

ABSTRACT: Coactivator complexes TFIID and SAGA recruit TATA-binding protein (TBP), while SAGA also enhances transcription by histone acetylation via the HAT Gcn5. It was proposed that most yeast genes depend exclusively on TFIID, with only ~10% requiring cumulative contributions by SAGA and TFIID for efficient transcription. It was further suggested that genes induced by Gcn4, transcriptional activator of amino acid biosynthetic genes induced by amino acid starvation, depend on the HAT, but not TBP-recruitment function of SAGA. At odds with this model, ChIP-sequencing of TBP and Pol II subunit Rpb1 revealed that deleting SPT3 or SPT8, but not GCN5, reduced TBP binding at most Gcn4 target genes, whereas deleting GCN5 selectively impaired promoter histone eviction; and all three SAGA mutations reduced transcription comparably. Nuclear depletion of TFIID subunit Taf1 generally reduced TBP recruitment at these and most other SAGA-dependent genes only in cells lacking Spt3 or Spt8. We conclude that SAGA is crucial for TBP recruitment via Spt3/Spt8, beyond its role in histone acetylation, whereas TFIID plays an ancillary role for the Gcn4 transcriptome in amino acid-starved cells.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE280732 | GEO | 2025/07/16

REPOSITORIES: GEO

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Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8 [RNA-seq]

Project description:Transcription initiation by RNA polymerase II is facilitated by coactivators that recruit general initiation factors to promoters. Coactivator complexes TFIID and SAGA recruit TATA-binding protein (TBP), while SAGA also enhances transcription by histone acetylation via the HAT Gcn5. It was proposed that most yeast genes depend exclusively on TFIID, with only ~10% requiring cumulative contributions by SAGA and TFIID for efficient transcription. It was further suggested that genes induced by Gcn4, transcriptional activator of amino acid biosynthetic genes induced by amino acid starvation, depend on the HAT but not the TBP-recruitment function of SAGA. At odds with this model, ChIP-sequencing of TBP and Pol II subunit Rpb1 revealed that deleting SPT3 or SPT8, but not GCN5, reduced TBP binding at many Gcn4 target genes. In contrast, deleting GCN5 but not SPT3 or SPT8 impaired promoter histone eviction at the highly remodeled subset of induced genes, whereas transcription was broadly reduced by all three SAGA mutations. Nuclear depletion of TFIID subunit Taf1 generally reduced TBP recruitment at these and most other SAGA-dependent genes only in cells lacking Spt3 or Spt8. We conclude that SAGA is crucial for TBP recruitment via Spt3/Spt8, beyond its role in histone acetylation, and functions non-redundantly with TFIID in the Gcn4 transcriptome of amino acid-starved cells.

2025-07-16 | GSE295279 | GEO

Differential requirements for Gcn5 and NuA4 HAT activities in the starvation-induced versus basal transcriptomes

Project description:The histone acetyltransferase (HAT) subunit of coactivator complex SAGA, Gcn5, is required for efficient eviction of promoter nucleosomes at certain highly expressed yeast genes, including those activated by transcription factor Gcn4 in amino acid-deprived cells; however, the importance of other HAT complexes in this process was poorly understood. Analyzing mutations that disrupt the integrity or activity of HAT complexes NuA4 or NuA3, or the HAT Rtt109, revealed that only NuA4 acts on par with Gcn5, and functions additively, in evicting and repositioning promoter nucleosomes and stimulating transcription of starvation-induced genes. NuA4 is generally more important than Gcn5, however, in promoter nucleosome eviction, TBP recruitment, and transcription at most other genes expressed constitutively. NuA4 also predominates over Gcn5 in stimulating TBP recruitment and transcription of genes categorized as principally dependent on the cofactor TFIID versus SAGA, except for the highly expressed subset encoding ribosomal proteins (RPs), where Gcn5 contributes strongly to PIC assembly and transcription. Both SAGA and NuA4 are recruited to promoter regions of SM-induced genes in a manner that appears to be feedback controlled by their HAT activities. Our findings reveal an intricate interplay between these two HATs in nucleosome eviction, PIC assembly, and transcription that differs between the starvation-induced and basal transcriptomes.

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Genome-wide regulation by TFIID and SAGA

Project description:TFIID and SAGA share a common set of TAFs, regulate chromatin, and deliver TBP to promoters. Here we examine their relationship within the context of the Saccharomyces cerevisiae genome-wide regulatory network. We find that while TFIID and SAGA make overlapping contributions to the expression of all genes, TFIID function predominates at ~90% and SAGA at ~10% of the measurable genome. Strikingly, SAGA-dominated genes are largely stress-induced and TAF-independent, and are down-regulated by the coordinate action of a variety of chromatin, TBP, and RNA polymerase II regulators. In contrast, the TFIID-dominated class is less regulated, but is highly dependent upon TAFs including those shared between TFIID and SAGA. These two distinct modes of transcription regulation might reflect the need to balance inducible stress responses with the steady output of housekeeping genes. Keywords = Taf1 Keywords = Spt3 Keywords = Gcn5

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Genome-wide regulation by TFIID and SAGA

2004-02-27 | GSE885 | GEO

The SAGA coactivator regulates the expression of nearly all genes transcribed by RNA polymerase II

Project description:The SAGA coactivator complex facilitates transcription initiation through chromatin-modifying activities and interaction with TBP. SAGA was suggested to regulate the expression of about 10% of yeast genes, leading to the longstanding distinction of SAGA-dominated from TFIID-dominated genes, depending on the complex used to recruit TBP to promoters. We reassessed the genome-wide localization of SAGA by using ChEC-seq and its role on transcription through quantification of newly-synthesized mRNA. Here we show that SAGA binds to the upstream activating sequences of a majority of yeast genes. Deletion analyses reveal a global role for SAGA in transcription and a synergistic effect of Spt3 (TBP-binding subunit) with the acetyltransferase Gcn5. Our data demonstrate that SAGA acts as a general cofactor required for essentially all RNA polymerase II transcription. Hence, differential gene regulation, largely attributed to either SAGA or TFIID dominancy, is not accurate, but instead depends on other features of genes promoters.

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Spt3 and Spt8 are involved in the formation of a silencing boundary by interacting with TATA-binding protein

Project description:In Saccharomyces cerevisiae, a heterochromatin-like chromatin structure called the silencing region is present at the telomere as a complex of Sir2, Sir3, and Sir4. Sir2 is a histone deacetylase, and Sir3 and Sir4 promote spreading of the silencing region at the telomere. Histone acetyltransferases restrict the silencing region. Here, we show that Spt3 and Spt8 block the spread of silencing regions. Spt3 and Spt8 are members of the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, which has histone acetyltransferase activity. Although both Spt3 and Spt8 interact with telomere-binding proteins (TBPs), Spt3 had a greater effect on genome-wide transcription. Mutant analysis showed that TBPs play an important role in boundary formation, in particular the interaction between Spt3 and TBPs.

2023-03-29 | GSE220290 | GEO

Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8

Project description:Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8

| PRJNA1180110 | ENA

Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8 [RNA-seq]

Project description:Coactivator SAGA plays a crucial role in TBP recruitment for the Gcn4 transcriptome via subunits Spt3/Spt8 [RNA-seq]

| PRJNA1254112 | ENA

Transcription profiling of fission yeast SAGA mutants shows that the SAGA complex controls the switch from proliferation to sexual differentiation through the opposing roles of its subunits Gcn5 and Spt8

Project description:The SAGA complex is a conserved multifunctional coactivator known to play broad roles in eukaryotic transcription. To gain new insights into its functions, we have performed biochemical and genetic analyses of SAGA in the fission yeast, Schizosaccharomyces pombe. Purification of the S. pombe SAGA complex showed that its subunit composition is identical to that of Saccharomyces cerevisiae. Analysis of S. pombe SAGA mutants revealed that SAGA has two opposing roles regulating sexual differentiation. First, in nutrient rich conditions, the SAGA histone acetyltransferase, Gcn5, represses ste11+, which encodes the master regulator of the mating pathway. In contrast, the SAGA subunit Spt8 is required for the induction of ste11+ upon nutrient starvation. Chromatin immunoprecipitation experiments suggest that these regulatory effects are direct, as SAGA is physically associated with the ste11+ promoter independent of nutrient levels. Genetic tests suggest that nutrient levels do cause a switch in SAGA function, as spt8? suppresses gcn5? with respect to ste11+ derepression in rich medium, whereas the opposite relationship, gcn5? suppression of spt8?, occurs during starvation. Thus, SAGA plays distinct roles in the control of the switch from proliferation to differentiation in S. pombe through the dynamic and opposing activities of Gcn5 and Spt8.

2008-11-19 | E-MTAB-53 | biostudies-arrayexpress

Genome-wide association of Sus1 with RNAPII and tRNA genes depends on the distinctive SAGA subunits Spt8 and Spt7

Project description:We have analyzed the global effect of the conserved transcription-mRNA export factor Sus1 on transcription and its association with chromatin. We used genomic run-on experiments to show that Sus has a broad impact on the stability of most RNA polymerase II-transcribed genes. Genome association of Sus1 by the chromatin immunoprecipitation technique showed that Sus1 was widely distributed throughout coding regions, tending to accumulate towards the 3â ends of highly transcribed transcription factor IID (TFIID) and Spt-Ada-Gcn5 acetyltransferase (SAGA) dependent genes. This accumulation depends on growth conditions, the transcriptional rate and whether the genes are TFIID- or SAGA-regulated. Validation of Sus1 occupancy data also revealed that Sus1 appears at tRNAs. Concomitantly, deletion of SUS1 leads to tRNA overexpression. In addition, we discovered that distinctive SAGA subunits Spt8 and Spt7 play a key role in Sus1 enrichment at the 3â ends of SAGA-regulated genes upon temperature shift and at tRNAs. Thus, our study identifies the molecular mechanisms by which a SAGA factor is recruited genome-wide, and provides evidence of a more general role for this conserved coactivator in eukaryotic transcription. Genome wide analysis of Sus1 in wild type and Spt7 and Spt8 deletion mutants using ChIP-exo and genomic run-on experiments

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