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Xrn2 accelerates termination by RNA polymerase II, which is underpinned by CPSF73 activity

ABSTRACT: Termination is a ubiquitous phase in every transcription cycle but is incompletely understood and a subject of debate. We have used gene editing as a new approach to address its mechanism through engineered conditional depletion of the 5’-3’ exonuclease, Xrn2, or the polyadenylation signal (PAS) endonuclease, CPSF73. The ability to rapidly control Xrn2 reveals a clear and general role for it in co-transcriptional degradation of 3’ flanking region RNA and transcriptional termination. This defect is characterised genome-wide, at high resolution, using native elongating transcript sequencing (mNET-seq). An Xrn2 effect on termination requires prior RNA cleavage and we provide evidence for this by showing that catalytically inactive CPSF73 cannot restore termination to cells lacking functional CPSF73. Notably, Xrn2 plays no significant role in either Histone or snRNA gene termination even though both RNA classes undergo 3’ end cleavage. In sum, efficient termination on most protein-coding genes involves CPSF73 mediated RNA cleavage and co-transcriptional degradation of polymerase-associated RNA by Xrn2. However, as CPSF73 loss caused more extensive read-through transcription than Xrn2 elimination, it likely plays a more underpinning role in termination.

ORGANISM(S): Homo sapiens

PROVIDER: GSE109003 | GEO | 2018/02/13

REPOSITORIES: GEO

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Xrn2 substrate mapping identifies torpedo loading sites and extensive premature termination of RNA pol II transcription

Project description:The exonuclease torpedo Xrn2 loads onto nascent RNA 5’-PO4 ends and chases down pol II to promote termination downstream of polyA sites. We report that Xrn2 is recruited to pre-initiation complexes and “travels” to 3’ ends of genes. Mapping of 5’-PO4 ends in nascent RNA identified Xrn2 loading sites stabilized by an active site mutant, Xrn2(D235A). Xrn2 loading sites are ~2-20 bases downstream of where CPSF73 cleaves at polyA sites and histone 3’ ends. We propose that processing of all mRNA 3’ ends comprises cleavage and limited 5’-3’ trimming by CPSF73 followed by hand-off to Xrn2. A similar hand-off occurs at tRNA 3’ ends where co-transcriptional RNAseZ cleavage generates novel Xrn2 substrates. Exonuclease-dead Xrn2 increased transcription in 3’ flanking regions by inhibiting polyA site-dependent termination. Surprisingly, the mutant Xrn2 also rescued transcription in promoter-proximal regions to the same extent as in 3’ flanking regions. eNET-seq revealed Xrn2-mediated degradation of sense and anti-sense nascent RNA within a few bases of the TSS where 5’-PO4 ends may be generated by decapping or endonucleolytic cleavage. These results suggest that a major fraction of pol II complexes terminate prematurely close to the start site under normal conditions by an Xrn2-mediated torpedo mechanism.

2022-11-17 | GSE217033 | GEO

Mammalian NET-seq reveals genome-wide nascent transcription coupled to RNA processing

Project description:We have generated single-nucleotide resolution, nascent transcription profiles from HeLa cells by developing Native Elongation Transcript sequencing technology for mammalian chromatin (mNET-seq). Our extensive data sets provide a substantial resource to study mammalian nascent transcript profiles. We reveal unanticipated phosphorylation states for RNA polymerase II C-terminal domain (Pol II CTD) at both gene ends. We also observe that following 5’ splice site cleavage by the spliceosome, upstream exon transcripts are tethered to Pol II CTD phosphorylated on the serine 5 position (S5P) which is accumulated over downstream exons. We further show that depletion of termination factors substantially reduces Pol II pausing at gene ends leading to termination defects. Remarkably termination factors play an additional promoter role by restricting non-productive RNA synthesis and redistributing Pol II CTD S2P to promoters. These data demonstrate that CTD phosphorylation is more dynamic and variably distributed across mammalian transcription units than previously envisaged. To monitor nascent RNA within the mammalian Pol II complex, and its association with different CTD phosphorylation states, we employed mNET-seq methodology on HeLa cells, complemented with direct sequencing of chromatin-bound RNA (ChrRNA-seq). mNET-seq was preformed using the antibodies 8WG16, CMA602, CMA603 and CMA601, which are specific for unphosphorylated CTD, Ser2 phosphorylation, Ser5 phosphorylation and all CTD isoforms, respectively. In another experiment, to evaluate the effect of transcription termination factors in nascent RNA production by Pol II, mNET-seq and complemented with ChrRNA-seq was preformed on HeLa cells transfected with siRNA against PTBP1, CPSF73, CstF64+CstF64tau or Xrn2, and the gene profiles were compared with profiles from HeLa transfected with siRNA for Luciferase generated by the same protocol.

2015-04-23 | E-GEOD-60358 | biostudies-arrayexpress

A unified allosteric/torpedo mechanism for transcriptional termination on human protein-coding genes

Project description:The so-called allosteric and torpedo models have been used for the past thirty years to explain how transcription terminates on protein-coding genes. The former invokes conformational changes in the transcription complex and the latter involves degradation of the downstream product of poly(A) signal (PAS) processing. Here, we describe a single mechanism incorporating features of both models. We show that CPSF73 is indispensable for transcriptional termination on protein-coding and its loss causes profound read-through genome-wide. CPSF73 functions upstream of allosteric modifications to the elongation complex that cause Pol II to slow down after the PAS. This state is enriched by rapid depletion of XRN2 and promoted by protein phosphatase 1 (PP1), the inhibition of which confers runaway read-through in the absence of XRN2. These allosteric changes facilitate XRN2-dependent termination, by aiding its capture of Pol II, rather than constituting a termination pathway in themselves. Our experiments unify the long-standing allosteric and torpedo models for transcriptional termination.

2020-01-21 | GSE137727 | GEO

Xrn2 accelerates termination by RNA polymerase II, which is underpinned by CPSF73 activity

Project description:Xrn2 accelerates termination by RNA polymerase II, which is underpinned by CPSF73 activity

| PRJNA429385 | ENA

mRNA decapping factors and the exonuclease Xrn2 function in widespread premature termination of RNA polymerase II transcription

Project description:We report a function of human mRNA decapping factors in control of transcription by RNA polymerase II. Decapping proteins Edc3, Dcp1a and Dcp2 and the termination factor TTF2 co-immunoprecipitate with Xrn2, the nuclear 5'-3' exonuclease torpedo that facilitates transcription termination at the 3' ends of genes. Dcp1a, Xrn2 and TTF2 localize near transcription start sites (TSSs) by ChIP-Seq. At genes with 5' peaks of paused pol II, knockdown of decapping or termination factors, Xrn2 and TTF2, shifted polymerase away from the TSS toward upstream and downstream distal positions. This re-distribution of pol II is similar in magnitude to that caused by depletion of the elongation factor Spt5. We propose that coupled decapping of nascent transcripts and premature termination by the torpedo mechanism is a widespread mechanism that limits bidirectional pol II elongation. Regulated co-transcriptional decapping near promoter-proximal pause sites followed by premature termination could control productive pol II elongation. RNA pol II (GSE30895: GSM766171), Xrn2, TTF2 and Dcp1a were localized by ChIP-Seq in HeLa cells. RNA pol II was localized in control HEK293 cells and cells infected with lentiviruses expressing a scrambled control shRNA (scr), and shRNAs targeting the following proteins: Xrn2, TTF2, Xrn2+TTF2, Edc3, Dcp1a, and Dcp2.

2012-04-04 | E-GEOD-36185 | biostudies-arrayexpress

Genome-wide R-loop analysis defines unique roles for DDX5, XRN2, and PRMT5 in DNA/RNA hybrid resolution

Project description:DDX5, XRN2, and PRMT5 have been shown to resolve DNA/RNA hybrids (R-loops) at RNA polymerase II transcription termination sites at few genomic loci. Herein, we perform genome-wide R-loop mapping using classical DNA/RNA immunoprecipitation and high-throughput sequencing (DRIP-seq) of loci regulated by DDX5, XRN2, and PRMT5. We observed hundreds to thousands of R-loop gains and losses at transcribed loci in DDX5-, XRN2-, and PRMT5-deficient U2OS cells. R-loop gains were characteristic of highly transcribed genes located at gene-rich regions, whereas R-loop losses were observed in low-density gene areas. DDX5, XRN2, and PRMT5 shared many R-loop gain loci at transcription termination sites, consistent with their coordinated role in RNA polymerase II transcription termination. DDX5-depleted cells had unique R-loop gain peaks near the transcription start site that did not overlap with those of siXRN2 and siPRMT5 cells, suggesting a role for DDX5 in transcription initiation independent of XRN2 and PRMT5. Moreover, we observed that the accumulated R-loops at certain loci in siDDX5, siXRN2, and siPRMT5 cells near the transcription start site of genes led to antisense intergenic transcription. Our findings define unique and shared roles of DDX5, XRN2, and PRMT5 in DNA/RNA hybrid regulation.

2020-08-08 | GSE155865 | GEO

XRN2

Project description:XRN2

| PRJNA769688 | ENA

Effects of transcription elongation rate and Xrn2 exonuclease activity on RNA polymerase II termination suggest widespread kinetic competition

Project description:Transcription termination was analyzed by anti RNA pol II ChIP-seq in isogenic human HEK293 cell lines that inducibly express a-amanitin resistant mutants of the RNA polymerase II large subunit with slow and fast elongation rates and in lines that inducbily over-express WT or an active site mutant of the RNA exonuclease "torpedo" Xrn2. Transcription termination zones were mapped by anti-pol II ChIP-seq under conditions where transcription elongation rate was increased or decreased by point mutations in the large subunit of the enzyme. Termination was also assayed under conditions where Xrn2 exonuclease activity was inhibited by over-expression of an active site mutant (D235A).

2015-11-19 | E-GEOD-72800 | biostudies-arrayexpress

Two distinct transcription termination modes dictated by promoters

Project description:Transcription termination determines the ends of transcriptional units and thereby ensures integrity of gene regulation. Here we perform genome-wide investigation of RNA polymerase II (Pol II) transcription termination in Caenorhabditis elegans and observe two distinct modes of termination. Whereas a subset of genes requires the exoribonuclease XRN2, a known termination factor, termination of other genes appears independent of, and refractory to, XRN2. Unexpectedly, promoters instruct the choice of termination mode, but XRN2-independent termination additionally requires a compatible region downstream of the 3’ end cleavage site. Hence, different termination mechanisms may affect different configurations of Pol II complexes dictated by promoters.

2018-02-05 | GSE97775 | GEO

The immediate impact of exoribonucleolysis on nuclear RNA processing, turnover and transcriptional control revealed by rapid depletion of DIS3, EXOSC10 or XRN2 from human cells

Project description:Cell-based studies of human ribonucleases traditionally relies on methods that deplete proteins slowly. To assess their immediate roles in nuclear RNA biology, we engineered cells where the 3’->5’ exoribonucleases of the exosome complex, Dis3 and EXOSC10, can be eliminated within 60 minutes. Loss of Dis3 has the greatest impact, causing thousands of enhancer RNAs, intragenic transcripts, promoter upstream transcripts (PROMPTs) and products of premature cleavage and polyadenylation (PCPA) to accumulate. Interestingly, EXOSC10 only targets these substrates when Dis3 is absent, which is explained by its rapid mis-localization to the nucleoplasm following Dis3 loss. Direct detection of EXOSC10 substrates revealed a more specific role in trimming of short 3’ extensions on ribosomal and small nucleolar RNAs. Finally, the 5’-3’ exoribonuclease, Xrn2, has little activity on exosome substrates, but promotes termination following PCPA. Interestingly, Xrn2 is not rate limiting for PROMPT termination providing a distinction between sense and anti-sense transcriptional regulation.

2019-03-06 | GSE120574 | GEO

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