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Hierarchical TAF1-dependent co-translational assembly of the basal transcription factor TFIID

ABSTRACT: Large heteromeric multiprotein complexes play pivotal roles at every step of gene expression in eukaryotic cells. Among them, the 20-subunits basal transcription factor TFIID nucleates RNA polymerase II preinitiation complex at gene promoters. Here, by combining systematic RNA-immunoprecipitation experiments, single-molecule imaging, proteomics and structure-function analyses, we show that TFIID is built using co-translational assembly. We discovered that all early steps of TFIID assembly, involving protein heterodimerization, happen during protein synthesis. Strikingly, we identify TAF1 – the largest protein in the complex – as a flexible scaffold subunit that co-translationally recruits preassembled TFIID submodules found populating the cytoplasm of cells. Consequently, TAF1 depletion leads to a cytoplasmic accumulation of TFIID building blocks. Altogether, our data suggest a multistep hierarchical model for TFIID biogenesis that culminates with the co-translational assembly on nascent TAF1 polypeptide, that works as a ‘driver’ subunit. We envision that this assembly strategy could be shared with other large heteromeric protein complexes.

INSTRUMENT(S): Orbitrap Exploris 480, LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Permanent Cell Line Cell

SUBMITTER: Luc Negroni

LAB HEAD: Laszlo Tora

PROVIDER: PXD036358 | Pride | 2023-07-04

REPOSITORIES: Pride

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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.

			Action	DRS
	211210_AB_Ech01_Rep1.msf	Msf
	211210_AB_Ech01_Rep1.raw	Raw
	211210_AB_Ech01_Rep2.msf	Msf
	211210_AB_Ech01_Rep2.raw	Raw
	211210_AB_Ech01_Rep3.msf	Msf

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Hierarchical TAF1-dependent co-translational assembly of the basal transcription factor TFIID

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