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Chaperonin CCT Checkpoint Function in Basal Transcription Factor TFIID Assembly

ABSTRACT: TFIID is a cornerstone of eukaryotic gene regulation. Distinct TFIID complexes with unique subunit composition exist and several TFIID subunits are shared with other complexes, conveying intricate cellular decision making to control subunit allocation and functional assembly of this essential transcription factor. However, the underlying molecular mechanisms remain poorly understood. Here, we used quantitative proteomics to examine TFIID submodules and assembly mechanisms in human cells. Structural and mutational analysis of the cytoplasmic TAF5/TAF6/TAF9 submodule identified novel interactions crucial for TFIID integrity, and for allocating TAF9 to TFIID or the SAGA co-activator complex. We discover a key checkpoint function for the chaperonin CCT, which specifically associates with nascent TAF5 for subsequent handover to TAF6/TAF9 and ultimate holo-TFIID formation. Our findings illustrate at the molecular level how multisubunit complexes are crafted in the cell, involving checkpoint decisions facilitated by a chaperone machine.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Hela Cell

SUBMITTER: Simona Antonova

LAB HEAD: Marc Timmers

PROVIDER: PXD011211 | Pride | 2022-03-02

REPOSITORIES: Pride

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			Action	DRS
	20161025_OR12_A4_TY_SA_TAF6_Cyto_GFP01.raw	Raw
	20161025_OR12_A4_TY_SA_TAF6_Cyto_GFP02.raw	Raw
	20161025_OR12_A4_TY_SA_TAF6_Cyto_GFP03.raw	Raw
	20161025_OR12_A4_TY_SA_TAF6_Cyto_NGFP01.raw	Raw
	20161025_OR12_A4_TY_SA_TAF6_Cyto_NGFP02.raw	Raw

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Project description:RNA polymerase II (Pol II) transcription initiation starts with the assembly of the preinitiation complex (PIC) on core promoters. The PIC is composed of six general transcription factors (GTFs). The recognition of the core promoter sequences by the TFIID GTF complex is the first step of the PIC assembly. In metazoans, holo-TFIID is composed of the TATA binding protein (TBP) and of 13 TBP associated factors (TAFs). Genetic depletion of different murine TAFs have shown that TAFs such as TAF7 or TAF10, can be either required, or dispensable for Pol II transcription, depending on different cellular contexts. In this report, we depleted TAF7 and/or TAF10 in the same cellular system; either in mesodermal progenitors during mouse development or in mESCs. In these two models, TAF7 depletion leads to a milder phenotype compared to TAF10 depletion. As TAF10 is also a subunit of the transcriptional co-activator Spt-Ada-Gcn5 acetyl transferase (SAGA), we first showed that the difference in phenotype between the Taf7 and Taf10 mutant is not due to the SAGA effect, at least for mESCs. Immunoprecipitations coupled with mass spectrometry analyses from mESCs lysates assembly of holo-TFIID complex is rapidly affected after induction of the depletion. In line with the model of holo-TFIID sequential assembly, TAF10 depletion leads to an early defect with formation of the core-TFIID, while TAF7 depletion results in the formation of a TAF7-less TFIID. Thus, the difference in phenotype severity correlates with the degree of TFIID disassembly. Surprisingly, no major global changes in Pol II transcription could be observed after either TAF7 or TAF10 depletion. Our data suggest that the inducible loss of fully assembled canonical TFIID does not correlate with the lack of global Pol II transcription activity changes suggesting that partially assembled TFIID complexes can participate in Pol II transcription initiation, with only limited effect on Pol II nascent transcription.

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Chaperonin CCT Checkpoint Function in Basal Transcription Factor TFIID Assembly

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