Project description:Influenza virus polymerase transcribes or replicates the segmented RNA genome (vRNA) into respectively viral mRNA or full-length copies and initiates RNA synthesis by binding the conserved 3' and 5' vRNA ends (the promoter). In recent structures of promoter-bound polymerase, the cap-binding and endonuclease domains are configured for cap snatching, which generates capped transcription primers. Here, we present a FluB polymerase structure with a bound complementary cRNA 5' end that exhibits a major rearrangement of the subdomains within the C-terminal two-thirds of PB2 (PB2-C). Notably, the PB2 nuclear localization signal (NLS)- containing domain translocates ~90 A ̊ to bind to the endonuclease domain. FluA PB2-C alone and RNA-free FluC polymerase are similarly arranged. Biophysical and cap-dependent endonuclease assays show that in solution the polymerase explores different conformational distributions depending on which RNA is bound. The inherent flexibility of the polymerase allows it to adopt alternative conformations that are likely important during polymerase maturation into active progeny RNPs.</br></br>Extra contact information:</br><a href="mailto:cusack@embl.fr">Stephen Cusack</a>, EMBL Grenoble Outstation, Unit of Virus Host-Cell Interactions, France ( corresponding author and lab head )
Project description:Analyses of AP-MS experiments performed in HEK 293T cells infected with the influenza A/WSN/33 virus. In half of the experiments the virus was modified to contain a C-terminal Strep tag on the polymerase subunit PB2. Full details in York et al. 'Interactome analysis of the influenza A virus transcription/replication machinery identifies protein phosphatase 6 as a cellular factor required for efficient virus replication.'
Project description:During influenza A virus (IAV) infections, viral proteins are targeted by cellular E3 ligases for modification with ubiquitin. Here, we decipher and functionally explore the ubiquitin landscape of the IAV polymerase during infection of human alveolar epithelial cells by applying mass spectrometry analysis of immuno-purified K-ε-GG- (di-glycyl)-remnant-bearing peptides. We identified 59 modified lysines across all three subunits of the viral polymerase of which 17 distinctively affected mRNA transcription, vRNA replication and the generation of recombinant viruses via non-proteolytic mechanisms. Moreover, our results demonstrate that the ubiquitinated residue K578 in the PB1 thumb domain is crucial for the dynamic structural transitions of the viral polymerase that are required for vRNA replication. Mutations K578A and K578R impeded the steps of cRNA stabilization and vRNA transcription, respectively, and affected NP binding as well as polymerase dimerization. Collectively, our results indicate that ubiquitin-mediated disruption of the charge-dependent interaction between PB1-K578 and PB2-E72 is required to coordinate polymerase dimerization and facilitate vRNA replication, which demonstrates that IAV exploit the cellular ubiquitin system to modulate the activity of the viral polymerase for the regulation of viral replication.
Project description:Increased metabolic activity usually provides energy and nutrients for biomass synthesis and is indispensable for the progression of the cell cycle. Here, we found an unexpected role for α-ketoglutarate (αKG) generation in regulating cell cycle gene transcription. A reduction in cellular αKG levels triggered by malic enzyme 2 (ME2) or isocitrate dehydrogenase 1 (IDH1) depletion leads to a pronounced arrest in G1 phase, while αKG supplementation promotes cell cycle progression. Mechanistically, αKG directly binds to RNA polymerase II (RNAPII), increasing the level of RNAPII binding to the cyclin D1 gene promoter, consequently enhancing cyclin D1 transcription. Notably, αKG addition is sufficient to restore cyclin D1 expression in ME2- or IDH1- depleted cells, facilitating cell cycle progression and proliferation in these cells. Therefore, our findings reveal a previously unappreciated function of αKG in gene transcriptional regulation and cell cycle control.
Project description:tRNA genes are transcribed by RNA polymerase III (RNAPIII). During recent years it has become clear that RNAPIII activity is strictly regulated by the cell in response to environmental cues and the homeostatic status of the cell. However, the molecular mechanisms that control RNAPIII activity to regulate the amplitude of tDNA transcription in normally cycling cells are not well understood. Here, we show that tRNA levels fluctuate during the cell cycle and reveal the underlying molecular mechanism. The cyclin Clb5 recruits the cyclin dependent kinase Cdk1 to tRNA genes to boost tDNA transcription during S phase. At tDNA genes, Cdk1 promotes the recruitment of TFIIIC, stimulates the interaction between TFIIIB and TFIIIC, and increases the dynamics of RNA polymerase III in vivo. Furthermore, we identified Bdp1 as an important Cdk1 substrate in this process. Preventing Bdp1 phosphorylation prevented cell cycle-dependent recruitment of TFIIIC and abolished the cell cycle-induced increase in tDNA transcription. Our findings demonstrate that under optimal growth conditions Cdk1 gates tRNA synthesis in S phase by regulating the RNAPIII machinery, revealing a direct link between the cell cycle and RNAPIII activity.
Project description:RNA polymerase II promoter-proximal pausing is orchestrated by a ribonucleoprotein complex scaffolded by the noncoding RNA Rn7sk. However, how this interruption of transcription is mechanistically linked to RNA production remains largely unknown. Here, we show that forcing the pause release by germ-line deletion of Rn7sk was embryonic lethal, yet conditional deletion of Rn7sk enhanced stem cell differentiation in skin. To explore the immediate transcriptional mechanisms underpinning enhanced differentiation, we metabolically labelled newly-synthesized RNAs after Rn7sk deletion. Unexpectedly, forced pause release robustly repressed transcription specifically at cell cycle regulators, in the absence of chromatin remodeling at promoters and enhancers. Our results indicate that polymerase pausing affords the core elongation machinery time to properly assemble, and forced elongation triggers splicing defects and nuclear RNA decay. Cell cycle regulators appear highly sensitive to mis-regulation of the elongation machinery due to unique genomic features of high promoter accessibility and low GC–content in the gene body. Transcriptional pausing thus serves as a rate-limiting step in controlling cell division.
Project description:RNA polymerase II promoter-proximal pausing is orchestrated by a ribonucleoprotein complex scaffolded by the noncoding RNA Rn7sk. However, how this interruption of transcription is mechanistically linked to RNA production remains largely unknown. Here, we show that forcing the pause release by germ-line deletion of Rn7sk was embryonic lethal, yet conditional deletion of Rn7sk enhanced stem cell differentiation in skin. To explore the immediate transcriptional mechanisms underpinning enhanced differentiation, we metabolically labelled newly-synthesized RNAs after Rn7sk deletion. Unexpectedly, forced pause release robustly repressed transcription specifically at cell cycle regulators, in the absence of chromatin remodeling at promoters and enhancers. Our results indicate that polymerase pausing affords the core elongation machinery time to properly assemble, and forced elongation triggers splicing defects and nuclear RNA decay. Cell cycle regulators appear highly sensitive to mis-regulation of the elongation machinery due to unique genomic features of high promoter accessibility and low GC–content in the gene body. Transcriptional pausing thus serves as a rate-limiting step in controlling cell division.