Project description:Transcription by RNA polymerase I (RNAPI) represents most of the transcriptional activity in eukaryotic cells and is associated with the production of mature ribosomal RNA (rRNA). As several rRNA maturation steps are coupled to RNAPI transcription, the rate of RNAPI elongation directly influences processing of nascent pre-rRNA, and changes in RNAPI transcription rate can result in alternative rRNA processing pathways in response to growth conditions and stress. However, factors and mechanisms that control RNAPI progression by influencing transcription elongation rate remain poorly understood. Our project is to show that the conserved RNA-binding Seb1 is a pausing-promoting factor for RNA polymerases I to control cotranscriptional RNA processing. Here, we did a proximity dependent biotinylation followed by mass spectrometry (PDB-MS) of the Seb1 protein in order to assess for physical interactions with the RNAPI transcription machinery. A mutant E. coli BirA enzyme is fused to the Seb1 protein. This mutant version of BirA uses biotin to catalyze the formation of biotinoyl-5′-AMP (bioAMP), thereby generating a ‘cloud’ of activated biotin molecules that can react with free primary amines (most often lysine residues) of neighboring proteins. This experiment will support the conclusion that Seb1 is located at the rDNA locus.
Project description:Termination of RNA polymerase II (Pol II) transcription is a key step, that is important for 3’end formation of functional mRNA, mRNA release and Pol II recycling. Even so, this underlying termination mechanism is not yet understood. Here, we demonstrate that the conserved and essential termination factor Seb1 interacts with Pol II near the end of the RNA exit channel and the Rpb4/7 stalk. Furthermore, the Seb1 interaction surface with Pol II largely overlaps with that of the elongation factor Spt5. Notably, Seb1 co-transcriptional recruitment is dependent on Spt5 de-phosphorylation by the conserved PP1 phosphatase Dis2, which also de-phosphorylates threonine 4 within the Pol II heptad repeated C-terminal domain. We propose that Dis2 orchestrates the transition from elongation to termination phase during the transcription cycle by mediating elongation to termination factor exchange and de-phosphorylation of Pol II C-terminal domain.
Project description:Termination of Pol II transcription is an important step in the transcription cycle and is responsible for dislodgement of polymerase from DNA which leads to the release of a functional transcript. Recent studies have identified key players important for termination and showed a conserved domain that interacts with the phosphorylated C-terminus of Pol II (CTD-Interacting-Domain, CID) to constitute a common feature of these proteins. However, the mechanism by which transcription termination is achieved, is not understood. Using genome-wide methods, we demonstrate that the fission yeast CID protein Seb1 is essential for termination of protein-coding and non-coding genes through interacting with S2-phosphorylated Pol II and nascent RNA. Furthermore, we present the crystal structures of the Seb1 CTD- and RNA-binding modules. Unexpectedly, the latter reveals a novel intertwined two-domain arrangement of a canonical RRM and a second domain. These results provide important insights into the mechanism underlying eukaryotic transcription termination.
Project description:Termination of RNAPII transcription is associated with RNA 3â end formation. For coding genes, termination is initiated by the cleavage/polyadenylation machinery. In contrast, a majority of noncoding transcription events in S. cerevisiae do not rely on RNA cleavage for termination, but instead terminate via a pathway that requires the Nrd1-Nab3-Sen1 (NNS) complex. Here we show that the S. pombe ortholog of Nrd1, Seb1, does not function in NNS-like termination, but promotes polyadenylation site selection of coding and noncoding genes. We found that Seb1 associates with 3â end processing factors, is enriched at the 3â end of genes, and binds RNA motifs downstream of cleavage sites. Importantly, a deficiency in Seb1 resulted in widespread changes in 3â UTR length as a consequence of increased alternative polyadenylation. Given that Seb1 levels affected the recruitment of conserved 3â end processing factors, our findings indicate that the conserved RNA-binding protein Seb1 co-transcriptionally controls alternative polyadenylation. Two biological replicates of Seb1 and Control (parental strain) CRAC experiments
Project description:Transcription by RNA polymerase I (RNAPI) represents the majority of the transcriptional activity in eukaryotic cells and is associated with the production of mature ribosomal rRNAs (rRNAs). As several rRNA maturation steps are coupled to RNAPI transcription, the rate of RNAPI elongation directly influences processing of nascent rRNA, and changes in RNAPI transcription rate can result in alternative rRNA processing pathways in response to growth conditions and stress. However, factors and mechanisms that control RNAPI progression by influencing transcription elongation rate remain poorly understood. We show here that the conserved fission yeast RNA-binding protein Seb1 associates with the RNAPI transcription machinery and promotes RNAPI pausing states along the rDNA. The overall faster progression of RNAPI at the rDNA in Seb1-deficient cells impaired cotranscriptional rRNA processing and the production of mature rRNAs. Given that Seb1 also influences pre-mRNA processing by modulating RNAPII progression, our findings unveil Seb1 as a pausing-promoting factor for RNA polymerases I and II to control cotranscriptional RNA processing.
Project description:Termination of RNAPII transcription is associated with RNA 3’ end formation. For coding genes, termination is initiated by the cleavage/polyadenylation machinery. In contrast, a majority of noncoding transcription events in S. cerevisiae do not rely on RNA cleavage for termination, but instead terminate via a pathway that requires the Nrd1-Nab3-Sen1 (NNS) complex. Here we show that the S. pombe ortholog of Nrd1, Seb1, does not function in NNS-like termination, but promotes polyadenylation site selection of coding and noncoding genes. We found that Seb1 associates with 3’ end processing factors, is enriched at the 3’ end of genes, and binds RNA motifs downstream of cleavage sites. Importantly, a deficiency in Seb1 resulted in widespread changes in 3’ UTR length as a consequence of increased alternative polyadenylation. Given that Seb1 levels affected the recruitment of conserved 3’ end processing factors, our findings indicate that the conserved RNA-binding protein Seb1 co-transcriptionally controls alternative polyadenylation.