Project description:Yeast mRNAs are polyadenylated at multiple sites in their 3’ untranslated regions (3’UTRs), and poly(A) site usage is regulated by the rate of transcriptional elongation by RNA polymerase II (Pol II). Slow Pol II derivatives favor upstream poly(A) sites and fast Pol II derivatives favor downstream poly(A) sites. Transcriptional elongation and polyadenylation are linked at the nucleotide level, presumably reflecting Pol II dwell time at each residue that influences the level of polyadenylation. Here, we investigate the relationship between Pol II pause sites and poly(A) sites within 3’UTRs.
Project description:To study the impact of the RNA polymerase II (Pol II) elongation rate on gene expression, we used CRISPR-Cas9 genome editing in S. pombe to generate a "slow" Pol II mutant with decreased elongation rate. Although the mutation is well tolerated as far as cell growth is concerned, transcriptomic analyses revealed that the slow mutant tends to terminate transcription prematurely. We distinguished two mechanisms by which premature termination affects gene expression in the slow mutant: It either (1) shortens 3'UTR, or (2) derepresses protein coding genes by prematurely terminating upstream interfering RNAs. Strikingly, the genes affected by these mechanisms are enriched for genes involved in phosphate uptake and purine synthesis, two processes essential for the maintenance of the nucleotide pool of the cell. Together with evidences that nucleotides are conditional for Pol II processive elongation, our results suggest that Pol II elongation rate acts as both sensor and effector in response to nucleotide depletion.
Project description:Yeast mRNAs are polyadenylated at multiple sites in their 3' untranslated regions (3' UTRs), and poly(A) site usage is regulated by the rate of transcriptional elongation by RNA polymerase II (Pol II). Slow Pol II derivatives favor upstream poly(A) sites, and fast Pol II derivatives favor downstream poly(A) sites. Transcriptional elongation and polyadenylation are linked at the nucleotide level, presumably reflecting Pol II dwell time at each residue that influences the level of polyadenylation. Here, we investigate the effect of Pol II elongation rate on pausing patterns and the relationship between Pol II pause sites and poly(A) sites within 3' UTRs. Mutations that affect Pol II elongation rate alter sequence preferences at pause sites within 3' UTRs, and pausing preferences differ between 3' UTRs and coding regions. In addition, sequences immediately flanking the pause sites show preferences that are largely independent of Pol II speed. In wild-type cells, poly(A) sites are preferentially located < 50 nucleotides upstream from Pol II pause sites, but this spatial relationship is diminished in cells harboring Pol II speed mutants. Based on a random forest classifier, Pol II pause sites are modestly predicted by the distance to poly(A) sites but are better predicted by the chromatin landscape in Pol II speed derivatives. Transcriptional regulatory proteins can influence the relationship between Pol II pausing and polyadenylation but in a manner distinct from Pol II elongation rate derivatives. These results indicate a complex relationship between Pol II pausing and polyadenylation.
Project description:The objective of this study was to investigate the relationship between Pol I transcription elongation rate and ribosomal RNA processing in vivo by using a yeast strain containing a mutation in Pol I. This mutation, rpa190-F1205H, has been previously characterized to have a reduced elongation rate in vitro. Here, we used native elongating transcript sequencing (NET-seq) to determine the effect of this mutation on Pol I occupancy in vivo. Our findings demonstrate that this mutation induces increased Pol I pausing, especially in the first half of the 35S gene, and causes sequence-specific changes in Pol I occupancy.
Project description:Various histone modifications decorate nucleosomes within transcribed genes. Among these, monoubiquitylation of histone H2B (H2Bub1) and methylation of histone H3 on lysines 36 (H3K36me2/3) and 79 (H3K79me2/3) correlate positively with gene expression. By measuring the progression of the transcriptional machinery along genes within live cells, we now report that H2B monoubiquitylation occurs co-transcriptionally and accurately reflects the advance of RNA polymerase II (Pol II). In contrast, H3K36me3 and H3K79me2 are less dynamic and represent Pol II movement less faithfully. High resolution ChIP-seq reveals that H2Bub1 levels are selectively reduced at exons, and decrease in an exon-dependent stepwise manner towards the 3' end of genes. Exonic depletion of H2Bub1 in gene bodies is highly correlated with Pol II pausing at exons, suggesting elongation rate changes associated with intron-exon structure. Overall, our data shed light on the organization of H2Bub1 within transcribed genes, and single out H2Bub1 as a reliable marker for ongoing transcription elongation. H2Bub1 and H2B ChIP-seq in NT2 cells
Project description:Recent studies have revealed that the mRNA translation is punctuated by ribosomal pauses through the body of transcripts. However, little is known about its physiological significance and regulatory aspects. Here we present a multi-dimensional ribosome profiling approach to quantify the dynamics of initiation and elongation of 80S ribosomes across the entire transcriptome in mammalian cells. We show that a subset of transcripts have a significant pausing of 80S ribosome around the start codon, creating a major barrier to the commitment of translation elongation. Intriguingly, genes encoding ribosome proteins themselves exhibit an exceptionally high initiation pausing on their transcripts. Our studies also reveal that the initiation pausing is dependent on the 5M-bM-^@M-^Y untranslated region (5M-bM-^@M-^Y UTR) of mRNAs and subject to the regulation of mammalian target of rapamycin complex 1 (mTORC1). Thus, the initiation pausing of 80S ribosome represents a novel regulatory step in translational control mediated by nutrient signaling pathway. Monitor the translational status of transcriptome in mammalian cells under different conditions