Project description:The Paf1 complex (Paf1C) is a conserved transcription elongation factor that regulates transcription elongation efficiency, facilitates co-transcriptional histone modifications, and impacts molecular processes linked to RNA synthesis, such as polyA site selection. Coupling of the activities of Paf1C to transcription elongation requires its association with RNA polymerase II (Pol II). Mutational studies in yeast identified Paf1C subunits Cdc73 and Rtf1 as important mediators of Paf1C association with Pol II on active genes. While the interaction between Rtf1 and the general elongation factor Spt5 is relatively well-understood, the interactions involving Cdc73 have not been fully elucidated. Using a site-specific protein cross-linking strategy in yeast cells, we identified direct interactions between Cdc73 and two components of the Pol II elongation complex, the elongation factor Spt6 and the largest subunit of Pol II. Both of these interactions require the tandem SH2 domain of Spt6. We also show that Cdc73 and Spt6 can interact in vitro and that rapid depletion of Spt6 dissociates Paf1 from chromatin, altering patterns of Paf1C-dependent histone modifications genome-wide. These results reveal interactions between Cdc73 and the Pol II elongation complex and identify Spt6 as a key factor contributing to the occupancy of Paf1C at active genes in Saccharomyces cerevisiae.
Project description:The polymerase associated factor 1 complex (Paf1C) is a multifunctional epigenetic regulator of RNA polymerase II (Pol II) transcription. Paf1C controls gene expression by stimulating the placement of co-transcriptional histone modifications, influencing nucleosome occupancy in coding regions, facilitating transcription termination, and regulating nuclear export of RNAs. In this study, we investigate the extent to which these functions of Paf1C combine to influence the Saccharomyces cerevisiae transcriptome. Using conditions that enrich for unstable transcripts, we show that deletion of PAF1 affects all classes of Pol II-transcribed RNAs including multiple classes of noncoding transcripts. Gene ontology analysis revealed that mRNAs encoding genes involved in iron and phosphate homeostasis were differentially affected by deletion of PAF1. We further investigated these two groups of mRNAs with the goal of identifying overarching mechanisms of up and down-regulation in cells lacking Paf1. Our results indicate that only a subset of the observed changes result from loss of Paf1C-promoted histone modifications. We also found that transcription of the FET4 gene is differentially regulated by Paf1 and an upstream CUT. Together these data highlight the complexity of the epigenetic regulation of Pol II transcription imposed by Paf1C and identify a role for Paf1C in promoting CUT transcription.
Project description:The PAF complex (Paf1C) has been shown to regulate chromatin modifications, gene transcription, and PolII elongation. Here, we provide the first genome-wide analysis of chromatin occupancy by the entire PAF complex in mammalian cells. We show that Paf1C is recruited not only to promoters and gene bodies, but also to regions downstream of cleavage/polyadenylation (pA) sites at 3â ends, a profile that sharply contrasted with the yeast complex. Remarkably, our studies identified novel, subunit-specific links between Paf1C and regulation of alternative cleavage and polyadenylation (APA) and upstream antisense transcription. Moreover, we found that depletion of Paf1C subunits also resulted in the accumulation of RNA polymerase II (PolII) over gene bodies, which coincided with APA. Depletion of specific Paf1C subunits leads to global loss of histone H2B ubiquitylation, but surprisingly, there is little impact of Paf1C depletion on other histone modifications, including the tri-methylation of histone H3 on lysines 4 and 36 (H3K4me3 and H3K36me3), previously associated with this complex. Our results provide surprising differences with yeast, while unifying observations that link Paf1C with PolII elongation and RNA processing, and suggest that Paf1C could play a role in protecting transcripts from premature cleavage by preventing PolII accumulation at TSS-proximal pA sites. ChIP-seq, RNA-seq and 3'READS of Paf1C factors in mouse C2C12 myoblast cells
Project description:Release of promoter-proximal paused RNA polymerase II (Pol II) during early elongation is a critical step in transcriptional regulation in metazoan cells. Paused Pol II release is thought to require the kinase activity of cyclin-dependent kinase 9 (CDK9) for the phosphorylation of DRB sensitivity-inducing factor, negative elongation factor, and C-terminal domain (CTD) serine-2 of Pol II. We found that Pol II-associated factor 1 (PAF1) is a critical regulator of paused Pol II release, that positive transcription elongation factor b (P-TEFb) directly regulates the initial recruitment of PAF1 complex (PAF1C) to genes, and that the subsequent recruitment of CDK12 is dependent on PAF1C. These findings reveal cooperativity among P-TEFb, PAF1C, and CDK12 in pausing release and Pol II CTD phosphorylation. Comparison of the chromatin occupancy of [1] PAF1, CDC73, LEO1, CTR9, total Pol II, and CTD serine 2-phosphorylated Pol II by ChIP-seq in THP1 cells; [2] PAF1, Pol II, Pol II (ser-5p), CDK12, and CDK9 by ChIP-seq in control and PAF1 knockdown cells; [3] LEO1 and Pol II by ChIP-seq in control and flavopiridol treated THP1 cells.
Project description:The aim of this experiment is to assess the genome-wide occupancy of Bye1, TFIIS and RNA polymerase II in yeast Saccharomyces cerevisiae by ChIP-chip
Project description:The PAF1 complex (PAF1C) functions in multiple transcriptional processes involving RNA Polymerase II (Pol II). eRNAs and PROMPTs are pervasive transcripts transcribed by Pol II and rapidly degraded by the nuclear exosome complex after 3’ endonucleolytic cleavage by the Integrator complex (Integrator). Here we show that PAF1C has an unexpected role in the termination of eRNAs and PROMPTs that are cleaved 1-3 kb downstream of the transcription start site. Mechanistically, PAF1C facilitates recruitment of Integrator to sites of pervasive transcript cleavage, promoting timely cleavage and transcription termination. We also show that PAF1C recruits Integrator to coding genes, where PAF1C then dissociates from Integrator upon entry into processive elongation. Our results demonstrate an unexpected function for PAF1C in limiting the length and accumulation of pervasive transcripts that result from nonproductive transcription
Project description:Release of promoter-proximal paused RNA polymerase II (Pol II) during early elongation is a critical step in transcriptional regulation in metazoan cells. Paused Pol II release is thought to require the kinase activity of cyclin-dependent kinase 9 (CDK9) for the phosphorylation of DRB sensitivity-inducing factor, negative elongation factor, and C-terminal domain (CTD) serine-2 of Pol II. We found that Pol II-associated factor 1 (PAF1) is a critical regulator of paused Pol II release, that positive transcription elongation factor b (P-TEFb) directly regulates the initial recruitment of PAF1 complex (PAF1C) to genes, and that the subsequent recruitment of CDK12 is dependent on PAF1C. These findings reveal cooperativity among P-TEFb, PAF1C, and CDK12 in pausing release and Pol II CTD phosphorylation.
Project description:Transcription by RNA polymerase II is regulated by epigenetic modifications to the chromatin template. The mono-ubiquitylation of H2B is established during transcription elongation and broadly impacts chromatin architecture and gene expression. The Polymerase Associated Factor 1 complex (Paf1C) is required for H2B ubiquitylation through an unknown mechanism. Here, we find that a 66-amino acid histone modification domain (HMD) within the Rtf1 subunit of Paf1C promotes H2B ubiquitylation in cells lacking all Paf1C members and present the crystal structure of this domain. Using site-specific in vivo crosslinking, we show that Rtf1 directly interacts with the ubiquitin conjugase Rad6 through a conserved surface on the HMD. Through ChIP-exo analysis, we observe that enrichment of Paf1C correlates with H2B ubiquitylation, and that the HMD, Rad6 and Bre1 localize to H2B. Finally, we demonstrate that the HMD directly stimulates H2B ubiquitylation in a reconstituted system, arguing that Paf1C functions as a cofactor for Rad6-Bre1 mediated catalysis.
Project description:Cyclin-dependent kinase 12 (CDK12) interacts with Cyclin K to form a functional nuclear kinase that promotes processive transcription elongation through phosphorylation of the RNA polymerase II (Pol II) C-terminal domain (CTD). To gain a broader understanding of CDK12 cellular function, we used chemical-genetic and phosphoproteomic screening to identify a landscape of nuclear human CDK12 substrates, including regulators of transcription, chromatin organization, and RNA splicing. We further validated LEO1, a subunit of the PAF1 complex (PAF1C), as a bona fide cellular substrate of CDK12. Acute depletion of LEO1, or substituting LEO1 phosphorylation sites with alanine, attenuated PAF1C association with elongating Pol II and impaired processive transcription elongation. We also found that LEO1 interacts with, and is dephosphorylated by, the Integrator-PP2A complex (INTAC) and that INTAC promotes the association of PAF1C with Pol II. Together, this study reveals a previously unknown role for CDK12 and INTAC in regulating LEO1 phosphorylation for transcriptional regulation, providing important insights into gene transcription and its regulation.