Project description:The production of a functional mRNA is regulated at every step of transcription. An area not well-understood is the transition of RNA polymerase II from elongation to termination. The S. cerevisiae SR-like protein Npl3 functions to negatively regulate transcription termination by antagonizing the binding of polyA/termination proteins to the mRNA. In this study, Npl3 is shown to interact with the CTD and have a direct stimulatory effect on the elongation activity of the polymerase. The interaction is inhibited by phosphorylation of Npl3. In addition, Casein Kinase 2 was found to specifically phosphorylate Npl3 and affect its ability to compete against Rna15 (Cleavage Factor I) for binding to polyA signals. Our results suggest that phosphorylation of Npl3 promotes its dissociation from the mRNA/RNAP II, and contributes to the association of the polyA/termination factor Rna15. This work defines a novel role for Npl3 in elongation and its regulation by phosphorylation. Keywords: Gene expression on a tiling array
Project description:Mammalian SR proteins are a family of reversibly phosphorylated RNA binding proteins primarily studied for their roles in alternative splicing. While budding yeast lack alternative splicing, they do have three SR-like proteins: Npl3, Gbp2, and Hrb1. However, these have been primarily studied for their roles in mRNA export, leaving their potential roles in splicing largely unexplored. Here we combined high-density genetic interaction profiling and genome-wide splicing-sensitive microarray analysis to demonstrate that a single SR-like protein, Npl3, is required for efficient splicing of a large set of pre-mRNAs in Saccharomyces cerevisiae. We tested the hypothesis that Npl3 promotes splicing by facilitating co-transcriptional recruitment of splicing factors. Using chromatin immunoprecipitation, we showed that mutation of NPL3 reduces the occupancy of U1 and U2 snRNPs at Npl3-stimulated genes. This provides the first evidence that an SR protein can promote recruitment of splicing factors to chromatin.
Project description:Yeast Npl3 is a highly abundant RNA binding protein, related to metazoan SR proteins, with reported functions including transcription elongation, splicing and RNA 3’ end processing. To identify direct targets and functions for Npl3, we used UV crosslinking and analysis of cDNA (CRAC) to map precise RNA binding sites. Npl3 binds diverse RNA species, at sites indicative of roles in both early pre-mRNA processing and 3’ end formation on mRNAs and ncRNAs. Consistent with this, tiling array and RNAPII binding data revealed 3’ extended mRNA and snoRNA transcripts in the absence of Npl3. This reflected transcriptional readthrough by RNAPII, and extension and stabilization of cryptic unstable transcript (CUT) long noncoding RNAs. Transcription readthrough was widespread, often resulting in down-regulation of neighboring genes. We conclude that Npl3 is required for the formation of a termination-competent RNA, affecting both coding and noncoding RNAs.
Project description:Yeast Npl3 is a highly abundant RNA binding protein, related to metazoan SR proteins, with reported functions including transcription elongation, splicing and RNA 3’ end processing. To identify direct targets and functions for Npl3, we used UV crosslinking and analysis of cDNA (CRAC) to map precise RNA binding sites. Npl3 binds diverse RNA species, at sites indicative of roles in both early pre-mRNA processing and 3’ end formation on mRNAs and ncRNAs. Consistent with this, tiling array and RNAPII binding data revealed 3’ extended mRNA and snoRNA transcripts in the absence of Npl3. This reflected transcriptional readthrough by RNAPII, and extension and stabilization of cryptic unstable transcript (CUT) long noncoding RNAs. Transcription readthrough was widespread, often resulting in down-regulation of neighboring genes. We conclude that Npl3 is required for the formation of a termination-competent RNA, affecting both coding and noncoding RNAs.
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.