Project description:The human Negative Elongation Factor (NELF) is a four-subunit protein complex that inhibits the movement of RNA polymerase II (RNAPII) at an early elongation stage in vitro. NELF-mediated stalling of RNAPII also attenuates transcription of a number of inducible genes in human cells. To obtain a genome-wide understanding of human NELF-mediated transcriptional regulation in vivo, we carried out an exon-array study in T47D breast cancer cells with transient siRNA knockdown of individual NELF subunits. Upon depletion of NELF-A, -C, or -E, the vast majority of NELF-regulated genes were down-regulated. Many of the down-regulated genes encode proteins that play key roles in cell cycle progression. Consequently, NELF knockdown resulted in significant reduction in DNA synthesis and cell proliferation. Chromatin immunoprecipitation showed that NELF knockdown led to dissociation of RNAPII from the promoter-proximal region of the cell cycle-regulating genes. This was accompanied by decreased histone modifications associated with active transcription initiation (H3K9Ac) and elongation (H3K36Me3), as well as reduced recruitment of the general transcription factor TFIIB and increased overall histone occupancy at a subset of the down-regulated promoters. Lastly, our study indicates that NELF regulates alternative transcription initiation of Basigin gene (BSG) by differentially influencing RNAPII density at the two neighboring exons at the 5’ end of the gene. Taken together, our data suggest a diverse transcriptional consequence of NELF-mediated RNAPII pausing in the human genome.
Project description:Spt6 is a conserved factor that controls transcription and chromatin structure across the genome. Although viewed as an elongation factor, spt6 mutations allow transcription from within coding regions, suggesting that Spt6 also controls initiation. To comprehensively characterize the requirement for Spt6 in transcription, we have used four approaches: TSS-seq and TFIIB ChIP-nexus to assay transcription initiation, NET-seq to assay elongating RNAPII, and MNase-seq to assay nucleosome occupancy and positioning. Our results demonstrate that Spt6 represses transcription initiation at thousands of intragenic promoters. We characterize these intragenic promoters, and find some features conserved with genic promoters and other features that are distinct. Finally, we show that Spt6 regulates transcription initiation at most genic promoters and propose a model of initiation site competition to account for this. Together, our results demonstrate that Spt6 controls the fidelity of transcription initiation throughout the genome and reveal the magnitude of the potential for expressing alternative genetic information via intragenic promoters.
Project description:Complex functional coupling exists between transcriptional elongation and pre-mRNA alternative splicing. Pausing sites and changes in the rate of transcription by RNAPII may therefore have a fundamental impact in the regulation of alternative splicing. Here, we show that the elongation and splicing-related factor TCERG1 regulates alternative splicing of the apoptosis gene Bcl-x in a promoter-dependent manner. TCERG1 promotes the splicing of the short isoform of Bcl-x (Bcl-xs) through the SB1 regulatory element located in the first half of exon 2. Consistent with these results, we show evidence for in vitro and in vivo interaction of TCERG1 with the Bcl-x pre-mRNA. Transcription profile analysis reveals that the RNA sequences required for the effect of TCERG1 on Bcl-x alternative splicing coincide with a putative polymerase pause site. Furthermore, TCERG1 modifies the impact of a slow polymerase on Bcl-x alternative splicing. In support of a role for an elongation mechanism in the transcriptional control of Bcl-x alternative splicing, we found that TCERG1 modifies the amount of pre-mRNAs generated at distal regions of the endogenous Bcl-x. Most importantly, TCERG1 affects the rate of RNAPII transcription of endogenous human Bcl-x. We propose that TCERG1 modulates the elongation rate of RNAPII to relieve pausing, thereby activating the pro-apoptotic Bcl-xS 5’ splice site. ChIP-Seq
Project description:The super elongation complex (SEC) contains the positive transcription elongation factor b (P-TEFb) and a subcomplex, ELL2-EAF1, which stimulates transcription elongation by RNA polymerase II (Pol II). Here we report the cryo-EM structure of ELL2-EAF1 bound to a Pol II elongation complex at 2.8 Å resolution. The ELL2-EAF1 dimerization module directly binds the Pol II lobe, explaining how SEC delivers P-TEFb to Pol II. The same site on the lobe also binds the initiation factor TFIIF, consistent with SEC binding only after the transition from transcription initiation to elongation. Structure-guided functional analysis shows that elongation stimulation requires the dimerization module and an ELL2 protein linker that tethers this module to the Pol II protrusion. Our results show that SEC stimulates elongation allosterically and indicate that this stimulation involves stabilization of a further closed conformation of the Pol II active center cleft.
Project description:Cyclin-dependent kinase 7 (CDK7), part of the general transcription factor TFIIH, promotes gene transcription by phosphorylating the C-terminal domain of RNA polymerase II (RNA Pol II). Here, we combine rapid CDK7 kinase inhibition with multi-omics analysis to unravel the direct functions of CDK7 in human cells. CDK7 inhibition causes RNA Pol II retention at promoters, leading to decreased RNA Pol II initiation and immediate global downregulation of transcript synthesis. Elongation, termination, and recruitment of co-transcriptional factors are not directly affected. Although RNA Pol II, initiation factors, and Mediator accumulate at promoters, RNA Pol II complexes can also proceed into gene bodies without promoter-proximal pausing while retaining initiation factors and Mediator. Further downstream, RNA Pol II phosphorylation increases and initiation factors and Mediator are released, allowing recruitment of elongation factors and an increase in RNA Pol II elongation velocity. Collectively, CDK7 kinase activity promotes the release of initiation factors and Mediator from RNA Pol II, facilitating RNA Pol II escape from the promoter.
Project description:Chromatin places fundamental physical constraints on transcription (Gamarra and Narlikar, 2021). The PAF1 complex (PAF1C), a hexamer of PAF1, LEO1, CTR9, SKI8, CDC73 and RTF1, plays a critical role in transcription with incompletely understood mechanisms. During transcriptional elongation, PAF1C is one of the positive elongation factors in complex with RNA polymerase II (Pol II) to facilitate elongation through chromatin (Vos et al., 2018), but it is unclear yet if negative elongation factors are needed concurrently to restrain elongation. Here we show that besides decreasing elongation rate, LEO1 knockout in human K562 cells increases transcriptional readthrough and cellular level of C-terminal domain (CTD) phosphorylated Pol II while increases and decreases transcriptional output of several hundred genes, respectively. Mechanistic analyses taking proteomic, functional genomic and biochemical approaches discovered that PAF1C regulates transcriptional termination in part through recruiting PNUTS-PP1γ complex and facilitates Pol II transcriptional re-initiation through recruiting TOX4-PP1α complex. Moreover, Paf1 conditional knockout in mice severely blocks T cell development, increases cellular level of CTD phosphorylated Pol II, mainly decreases Pol II occupancy and transcriptional output in double positive T cells, and importantly, the regulation of re-initiation by PAF1C through TOX4-PP1α complex is conserved between mouse and human. Our results also suggest that PNUTS-PP1γ and TOX4-PP1α bind PAF1C to restrain Pol II elongation through chromatin. These findings not only establish PAF1C as a critical regulator of transcriptional termination and re-initiation besides elongation but also advanced current understanding of elongation.