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Requirements for RNA polymerase II preinitiation complex formation in vivo.

ABSTRACT: Transcription by RNA polymerase II requires assembly of a preinitiation complex (PIC) composed of general transcription factors (GTFs) bound at the promoter. In vitro, some GTFs are essential for transcription, whereas others are not required under certain conditions. PICs are stable in the absence of nucleotide triphosphates, and subsets of GTFs can form partial PICs. By depleting individual GTFs in yeast cells, we show that all GTFs are essential for TBP binding and transcription, suggesting that partial PICs do not exist at appreciable levels in vivo. Depletion of FACT, a histone chaperone that travels with elongating Pol II, strongly reduces PIC formation and transcription. In contrast, TBP-associated factors (TAFs) contribute to transcription of most genes, but TAF-independent transcription occurs at substantial levels, preferentially at promoters containing TATA elements. PICs are absent in cells deprived of uracil, and presumably UTP, suggesting that transcriptionally inactive PICs are removed from promoters in vivo.

SUBMITTER: Petrenko N

PROVIDER: S-EPMC6366898 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Requirements for preinitiation complex formation in vivo

Project description:Transcription by RNA polymerase (Pol) II requires assembly of a preinitiation complex (PIC) composed of general transcription factors (GTFs) bound at the core promoter. In vitro, the TATA-binding protein (TBP), TFIIB, TFIIF, and Pol II are essential for PIC formation and transcriptional initiation, whereas TFIIA, TFIIE, and TFIIH are not required under certain conditions. In addition, the PIC is stable in the absence of nucleotide triphosphates, and sequential addition of GTFs results in a series of partial PICs. Here, we analyze the roles of all GTFs in yeast cells by measuring PIC formation and Pol II transcription upon depletion of individual GTFs. All GTFs are essential for TBP binding and Pol II transcription in vivo, suggesting that partial PICs composed of GTF subsets do not exist at appreciable levels. In contrast, TBP-associated factors (TAFs) contribute to Pol II transcriptional activity at most (and perhaps all) genes, but TAF-independent transcription occurs at a substantial level, particularly at promoters lacking canonical TATA elements. Lastly, unlike the case in vitro, PICs are not observed in cells deprived of uracil, and presumably UTP, suggesting a mechanism that removes transcriptionally inactive PICs from promoters.

2019-02-27 | GSE122734 | GEO

Structure of an RNA polymerase II preinitiation complex.

Project description:The structure of a 33-protein, 1.5-MDa RNA polymerase II preinitiation complex (PIC) was determined by cryo-EM and image processing at a resolution of 6-11 Å. Atomic structures of over 50% of the mass were fitted into the electron density map in a manner consistent with protein-protein cross-links previously identified by mass spectrometry. The resulting model of the PIC confirmed the main conclusions from previous cryo-EM at lower resolution, including the association of promoter DNA only with general transcription factors and not with the polymerase. Electron density due to DNA was identifiable by the grooves of the double helix and exhibited sharp bends at points downstream of the TATA box, with an important consequence: The DNA at the downstream end coincides with the DNA in a transcribing polymerase. The structure of the PIC is therefore conducive to promoter melting, start-site scanning, and the initiation of transcription.

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Requirements for preinitiation complex formation in vivo

Project description:Requirements for preinitiation complex formation in vivo

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Polycomb repressive complex 1 (PRC1) disassembles RNA polymerase II preinitiation complexes.

Project description:Despite the important role of Polycomb in genome-wide silencing, little is known of the specific biochemical mechanism by which it inactivates transcription. Here we address how recombinant Polycomb repressive complex 1 (PRC1) inhibits activated RNA polymerase II preinitiation complex (PIC) assembly using immobilized H3K27-methylated chromatin templates in vitro. Recombinant PRC1 inhibited transcription, but had little effect on binding of the activator as reported previously. In contrast, Mediator and the general transcription factors were blocked during assembly or dissociated from preassembled PICs. Importantly, among the PIC components, Tata Binding Protein (TBP) was the most resistant to eviction by PRC1. Immobilized template experiments using purified PRC1, transcription factor II D (TFIID), and Mediator indicate that PRC1 blocks the recruitment of Mediator, but not TFIID. We conclude that PRC1 functions to block or dissociate PICs by interfering with Mediator, but leaves TBP and perhaps TFIID intact, highlighting a specific mechanism for PRC1 transcriptional silencing. Analysis of published genome-wide datasets from mouse embryonic stem cells revealed that the Ring1b subunit of PRC1 and TBP co-enrich at developmental genes. Further, genes enriched for Ring1b and TBP are expressed at significantly lower levels than those enriched for Mediator, TBP, and Ring1b. Collectively, the data are consistent with a model in which PRC1 and TFIID could co-occupy genes poised for activation during development.

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The positions of TFIIF and TFIIE in the RNA polymerase II transcription preinitiation complex.

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Position of the general transcription factor TFIIF within the RNA polymerase II transcription preinitiation complex.

Project description:The RNA polymerase (pol) II general transcription factor TFIIF functions at several steps in transcription initiation including preinitiation complex (PIC) formation and start site selection. We find that two structured TFIIF domains bind Pol II at separate locations far from the active site with the TFIIF dimerization domain on the Pol II lobe and the winged helix domain of the TFIIF small subunit Tfg2 above the Pol II protrusion where it may interact with upstream promoter DNA. Binding of the winged helix to the protrusion is PIC specific. Anchoring of these two structured TFIIF domains at separate sites locates an essential and unstructured region of Tfg2 near the Pol II active site cleft where it may interact with flexible regions of Pol II and the general factor TFIIB to promote initiation and start site selection. Consistent with this mechanism, mutations far from the enzyme active site, which alter the binding of either structured TFIIF domains to Pol II, have similar defects in transcription start site usage.

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Architecture of the RNA polymerase II preinitiation complex and mechanism of ATP-dependent promoter opening.

Project description:Yeast RNA polymerase II (Pol II) general transcription factor TFIIE and the TFIIH subunit Ssl2 (yeast ortholog of mammalian XPB) function in the transition of the preinitiation complex (PIC) to the open complex. We show that the three TFIIE winged-helix (WH) domains form a heterodimer, with the Tfa1 (TFIIEα) WH binding the Pol II clamp and the Tfa2 (TFIIEβ) tandem WH domain encircling promoter DNA that becomes single-stranded in the open complex. Ssl2 lies adjacent to TFIIE, enclosing downstream promoter DNA. Unlike previous proposals, comparison of the PIC and open-complex models strongly suggests that Ssl2 promotes DNA opening by functioning as a double-stranded-DNA translocase, feeding 15 base pairs into the Pol II cleft. Right-handed threading of DNA through the Ssl2 binding groove, combined with the fixed position of upstream promoter DNA, leads to DNA unwinding and the open state.

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TFIIB is only ∼9 A away from the 5'-end of a trimeric RNA primer in a functional RNA polymerase II preinitiation complex.

Project description:Recent X-ray crystallographic studies of Pol II in complex with the general transcription factor (GTF) IIB have begun to provide insights into the mechanism of transcription initiation. These structures have also shed light on the architecture of the transcription preinitiation complex (PIC). However, structural characterization of a functional PIC is still lacking, and even the topological arrangement of the GTFs in the Pol II complex is a matter of contention. We have extended our activity-based affinity crosslinking studies, initially developed to investigate the interaction of bacterial RNA polymerase with σ, to the eukaryotic transcription machinery. Towards that end, we sought to identify GTFs that are within the Pol II active site in a functioning PIC. We provide biochemical evidence that TFIIB is located within ∼9 Å of the -2 site of promoter DNA, where it is positioned to play a role in de novo transcription initiation.

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The transcription elongation factor TFIIS is a component of RNA polymerase II preinitiation complexes.

Project description:In this article, we provide direct evidence that the evolutionarily conserved transcription elongation factor TFIIS functions during preinitiation complex assembly. First, we identified TFIIS in a mass spectrometric screen of RNA polymerase II (Pol II) preinitiation complexes (PICs). Second, we show that the association of TFIIS with a promoter depends on functional PIC components including Mediator and the SAGA complex. Third, we demonstrate that TFIIS is required for efficient formation of active PICs. Using truncation mutants of TFIIS, we find that the Pol II-binding domain is the minimal domain necessary to stimulate PIC assembly. However, efficient formation of active PICs requires both the Pol II-binding domain and the poorly understood N-terminal domain. Importantly, Domain III, which is required for the elongation function of TFIIS, is dispensable during PIC assembly. The results demonstrate that TFIIS is a PIC component that is required for efficient formation and/or stability of the complex.

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Genome-wide regulations of the preinitiation complex formation and elongating RNA polymerase II by an E3 ubiquitin ligase, San1.

Project description:San1 is an E3 ubiquitin ligase involved in nuclear protein quality control via its interaction with intrinsically disordered proteins for ubiquitylation and 26S proteasomal degradation. Since a number of transcription/chromatin regulatory factors contain intrinsically disordered domains and can be inhibitory to transcription when in excess, San1 might be involved in regulation of transcription. To address this, we carried out ChIP-seq (Chromatin immunoprecipitation sequencing) here to analyze the role of San1 in genome-wide association of TBP (TATA-box binding protein that nucleates the preinitiation complex formation at the promoter for transcription initiation) and RNA polymerase II (that is recruited to the promoter by TBP and subsequently engaged in transcription elongation at the coding sequence for mRNA biosynthesis). Our results reveal the genome-wide role of San1 in facilitating the recruitment of TBP to the promoter, thus indicating its involvement in promoting the preinitiation complex formation for transcription initiation. Further, we find the global role of San1 in regulating RNA polymerase II at the coding sequence.

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