Project description:Transcription of many genes in metazoans is subject to polymerase pausing, which corresponds to the transient arrest of transcriptionally engaged polymerase. It occurs mainly at promoter proximal regions and is not well understood. In particular, a genome-wide measurement of pausing times at high resolution has been lacking. This is because relevant experimental techniques are mostly based on average polymerase occupancies across many cells which cannot discriminate between few slow polymerases and many quick polymerases at a position, since the data corresponds to the average of many cells. We present here an extension of the PRO-seq assay, which we termed time variant PRO-seq (TV-PRO-seq)based on a detailed analysis of the logics underlying PRO-seq, that achieves this goal.
Project description:Transcription regulation occurs frequently through promoter-associated pausing of RNA polymerase II (Pol II). We developed a Precision nuclear Run-On and sequencing assay (PRO-seq) to map the genome-wide distribution of transcriptionally-engaged Pol II at base-pair resolution. Pol II accumulates immediately downstream of promoters, at intron-exon junctions that are efficiently used for splicing, and over 3' poly-adenylation sites. Focused analyses of promoters reveal that pausing is not fixed relative to initiation sites nor is it specified directly by the position of a particular core promoter element or the first nucleosome. Core promoter elements function beyond initiation, and when optimally positioned they act collectively to dictate the position and strength of pausing . We test this ‘Complex Interaction’ model with insertional mutagenesis of the Drosophila Hsp70 core promoter. Identification of RNA polymerase active sites in Drosophila S2 cell line using PRO-seq method. Identification of transcription initiation sites in Drosophila S2 cell line using PRO-cap method. Identification of changes in RNA polymerase active sites on transgenic Hsp70 promoters upon disruption of DNA sequence elements in 3 transgenic fly lines using PRO-seq method.
Project description:RNA polymerase II (pol II) transcribes all protein-coding and many non-coding RNAs in the human genome. Pol II transcription initiation is governed by the Pre-Initiation Complex (PIC), which contains TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH, pol II, and Mediator. After initiation, pol II enzymes typically pause after transcribing less than 100 bases, and paused polymerases represent a common regulatory intermediate. Accordingly, paused pol II has been implicated in enhancer function, development and homeostasis, and diseases ranging from cancer to viral pathogenesis. Precisely how pol II promoter-proximal pausing is enforced and regulated remains unclear; however, protein complexes such as NELF and DSIF increase pausing whereas the activity of CDK9 (P-TEFb complex) correlates with pause release. To address specific mechanistic questions about pol II pausing and its regulation, we reconstituted human pol II promoter-proximal pausing in vitro, entirely with purified factors (no extracts). As expected, NELF and DSIF increased pol II pausing in vitro, whereas P-TEFb promoted pause release. Unexpectedly, the PIC alone was sufficient to reconstitute pol II pausing, suggesting that pausing is an inherent property of the PIC. In agreement, pol II pausing was lost upon replacement of the TFIID complex with TATA-binding protein (TBP); moreover, pausing was dependent upon TFIID subunits TAF1 and TAF2. TAF1/2 bind genomic DNA downstream of the pol II initiation site, invoking a “complex interaction” model for pausing. Consistent with this model, PRO-Seq experiments revealed increased transcription upon acute depletion (t=60 min) of TAF1 and TAF2 in human cells, and pol II pausing was disrupted at thousands of genes. Similar results were obtained in TAF1-depleted Drosophila S2 cells. Collectively, these data establish the general transcription factor TFIID as a genome-wide regulator of pol II promoter-proximal pausing.
Project description:We analyzed the breadth and functional relationships of RNA Polymerase II pausing across many human and mouse cell types to understand what roles RNA Polymerase II pausing plays in gene regulation. We identified a novel association of H2A.Z at the TSS of increasingly paused genes. We knocked down H2A.Z to test whether H2A.Z positively or negatively affects RNA Polymerase II pausing to find that pausing globally increased upon knockdown.
Project description:Transcription regulation occurs frequently through promoter-associated pausing of RNA polymerase II (Pol II). We developed a Precision nuclear Run-On and sequencing assay (PRO-seq) to map the genome-wide distribution of transcriptionally-engaged Pol II at base-pair resolution. Pol II accumulates immediately downstream of promoters, at intron-exon junctions that are efficiently used for splicing, and over 3' poly-adenylation sites. Focused analyses of promoters reveal that pausing is not fixed relative to initiation sites nor is it specified directly by the position of a particular core promoter element or the first nucleosome. Core promoter elements function beyond initiation, and when optimally positioned they act collectively to dictate the position and strength of pausing . We test this ‘Complex Interaction’ model with insertional mutagenesis of the Drosophila Hsp70 core promoter.
Project description:Biochemical studies have established that the four-subunit negative elongation factor (NELF) complex mediates RNA polymerase II (Pol II) pausing at promoter proximal regions. Genetic ablation of individual NELF subunits destabilizes the entire NELF complex and causes lethality of cultured cells, leading to the prevailing concept that NELF-mediated Pol II pausing is essential for cell survival. Using separation-of-function mutations, we show here that NELFB’s effects on cell proliferation can be uncoupled from its function in Pol II pausing. NELFB mutants localized in the cytoplasm and incapacitated in the NELF complex assembly still retain their ability to support cell proliferation and at least part of NELFB-dependent transcriptome. Furthermore, we demonstrate that cytoplasmic NELFB physically and functionally interacts with multiple pro-survival signaling kinases, most notably PI3K/AKT. Enforced activation of PI3K/AKT-related kinases largely rescues deficiency of NELFB-depleted cells in proliferation, but not Pol II pausing. Together, these data revise the current understanding of the growth impact of Pol II pausing and underscore multiplicity of the biological function of individual NELF subunits.