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Chaperone-mediated ordered assembly of the SAGA and NuA4 transcription co-activator complexes

ABSTRACT: Transcription initiation involves the coordinated activities of large multimeric complexes that are organized into functional modules. Little is known about the mechanisms and pathways that govern their assembly from individual components. We report here several principles governing the assembly of the highly conserved SAGA and NuA4 co-activator complexes. Using fission yeast, which contain two functionally non-redundant paralogs of the shared Tra1 subunit, we demonstrate that Tra1 contributes to scaffolding the entire NuA4 complex. In contrast, within SAGA, Tra1 specifically promotes the incorporation of the de-ubiquitination module (DUB), defining an ordered assembly pathway. Biochemical and functional analyses elucidated the mechanism by which Tra1 assemble differentially into SAGA or NuA4 and identified a small, conserved region of Spt20 that is both necessary and sufficient to anchor Tra1 within SAGA. Finally, we establish that Hsp90 and its cochaperone TTT are required for Tra1 de novo incorporation into both SAGA and NuA4, indicating that Tra1, a pseudokinase of the PIKK family, shares a dedicated chaperone machinery with its cognate kinases. Overall, our work brings mechanistic insights into the de novo assembly of transcriptional complexes through ordered pathways and reveals the contribution of dedicated chaperones to this process.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE128448 | GEO | 2019/09/30

REPOSITORIES: GEO

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Project description:Tra1 is a component of the Saccharomyces cerevisiae SAGA and NuA4 complexes and a member of the phosphatidylinositol 3-kinase (PI3K) related kinase family that contain a C- terminal PI3K domain followed by a ~ 35-residue FATC domain. We have characterized four alleles with single residue changes in the FATC domain. Of these tra1-L3733A had the most pronounced effects with phenotypes including temperature and cold sensitivity, and reduced growth in media containing ethanol, Calcofluor white, rapamycin, chloramphenicol and geneticin. Tra1-L3733A interacted at normal levels with components of the NuA4 and SAGA complexes, and did not significantly alter histone acetylation patterns. The tra1-L3733A allele resulted in two-fold or greater change in expression of approximately 11% of yeast genes in rich media. Of the 279 genes with increased expression, 175 were ribosomal subunits or involved in ribosomal function or biogenesis. Elevated levels of Pol I and Pol III transcripts were also observed. The phenotypes of the tra1-L3733A overlapped with but were not identical to strains containing deletions of SAGA or NuA4 components or with strains containing mutations in the PI3K domain. Our finding that the double mutant allele, tra1-SRR3413/L3733A with alterations in the PI3K and FATC domains, resulted in wild type growth, suggests a model whereby the FATC domain negatively regulates the activity of the PI3K domain. Expression of genes involved in ribosome biosynthesis, other than the ribosomal subunits themselves, returned to near normal levels in the double mutant strain. We also characterized tra1-G3745, which contains an additional glycine residue following the normal C-terminal phenylalanine. This allele did not support viability and showed severe dominant negative effects. In contrast to what was observed for tra1-L3733A, tra1-G4745 resulted in decreased expression of genes required for ribosome biogenesis and did not interact with Esa1 or Spt7. Three biological replicate experiments including one dye-swap were performed for yeast strains CY3003(TRA1::Tn10LUK with IB150(myc9-tra1_L3733A-YCplac111)) and CY3015(TRA1::Tn10LUK with IB157(myc9-tra1_SRR3413_L3733A-YCplac111)) with reference to CY2706(TRA1::Tn10LUK with 1980(myc9-TRA1-YCplac111)). Similarly, three biological replicate experiments including one dye-swap were performed for yeast strain CY3019(TRA1::Tn10LUK with 1259(myc-TRA1-YCplac111) and IB162(myc9-tra1_G3745-YCplac111)) with reference to CY3020(TRA1::Tn10LUK with 1259(myc-TRA1-YCplac111) and IB160(myc9-TRA1-YCplac111)).

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Chaperone-mediated ordered assembly of the SAGA and NuA4 transcription co-activator complexes

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