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Distinct functions of three chromatin remodelers in activator binding and preinitiation complex assembly

ABSTRACT: ATP-dependent chromatin remodelers (CRs), including SWI/SNF, RSC and Ino80C in budding yeast, are thought to stimulate transcription by repositioning or evicting promoter nucleosomes. The relative importance of these CRs in stimulating activator binding and recruitment of TATA-binding protein (TBP) to promoters is incompletely understood. Examining mutants depleted of the catalytic subunits of these CRs, we determined that RSC and Ino80C stimulate binding of transcription factor Gcn4 to nucleosome-depleted regions, or linkers between genic nucleosomes, at multiple target genes activated by Gcn4 in amino acid-starved cells, frequently by evicting nucleosomes from the Gcn4 binding motifs. At some genes, SWI/SNF functionally complements RSC, while opposing RSC at others to limit Gcn4 binding. The CRs in turn are recruited by Gcn4 to establish positive or negative feedback loops that control Gcn4 binding. The three CRs also cooperate to enhance TBP recruitment, again involving nucleosome depletion, at both Gcn4 target genes and highly expressed ribosomal protein genes, whereas only RSC and Ino80C act broadly throughout the genome to enhance this key step in preinitiation complex assembly. Our findings illuminate functional cooperation among multiple CRs in regulating activator binding and promoter activation.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE192592 | GEO | 2021/12/29

REPOSITORIES: GEO

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Project description:SWI/SNF-family chromatin remodelling complexes conduct nucleosome sliding and ejection to provide DNA-binding proteins access to their sites in chromatin. RSC is an essential and abundant SWI/SNF-family chromatin remodeller from S. cerevisiae that both slides and ejects nucleosomes. However, how ejection versus sliding is chosen, regulated and implemented by any remodeller remains largely unknown. The RSC catalytic subunit Sth1 conducts ATP-dependent DNA translocation, pumping DNA around the nucleosome, providing a property that might underlie both sliding and ejection. Sth1 shares with other SWI/SNF-family ATPases direct binding to two nuclear actin-related proteins (ARPs), but how ARPs impact DNA translocation, sliding and ejection is unknown. Here, we reveal that nucleosome ejection by RSC requires ARPs, and that ARPs improve ‘coupling’ – the efficiency of DNA translocation by Sth1 relative to ATP hydrolysis – thus, enhancing DNA translocation. We further characterize two domains within Sth1 (termed PTH and P1), showing they separately regulate ATP hydrolysis or ‘coupling’, respectively. Interestingly, gain-of-function PTH or P1 mutations suppress arpΔ lethality, and improve ATPase or coupling activities, enabling Sth1 to efficiently slide and eject nucleosomes without ARPs. Moreover, PTH mutations greatly improved DNA translocation velocity. Overall, our results provide a logic for regulating nucleosome sliding versus ejection: both modes involve DNA translocation, but ejection requires a higher magnitude. Here, low-to-moderate ATPase and coupling activity integrate to confer low-to-moderate sliding, whereas high ATPase and/or coupling combine to provide efficient and rapid DNA translocation, consistent with the simultaneous rupture of multiple histone-DNA contacts, causing histone loss/ejection. Our discovery of an ARP module and regulatory domains that regulate sliding and ejection suggests a mechanistic platform through which activators and histone epitopes may guide the remodelling outcome of SWI/SNF-family chromatin remodellers.

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Distinct functions of three chromatin remodelers in activator binding and preinitiation complex assembly

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