The Paf1 complex broadly impacts the transcriptome of Saccharomyces cerevisiae
Ontology highlight
ABSTRACT: 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: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:In vitro studies identified various factors including P-TEFb, SEC, SPT6, PAF1, DSIF, and NELF functioning at different stages of transcription elongation driven by RNA polymerase II (RNA Pol II). What remains unclear is how these factors cooperatively regulate pause/release and productive elongation in the context of living cells. Using an acute 5 protein-depletion approach, prominent release and a subsequent increase in mature transcripts, whereas long genes fail to yield mature transcripts due to a loss of processivity. Mechanistically, loss of SPT6 results in loss of PAF1 complex (PAF1C) from RNA Pol II, leading to NELF-bound RNA Pol II release into the gene bodies. Furthermore, SPT6 and/or PAF1 depletion impairs heat shock-induced pausing, pointing to a role for SPT6 in regulating RNA Pol II pause/release through the recruitment of PAF1C during the early elongation.
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 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: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.
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.
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.
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.
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.