Project description:Transcription termination in Saccharomyces cerevisiae can be performed by at least two distinct pathways and is directed by the phosphorylation status of the carboxy-terminal domain (CTD) of RNA polymerase II (Pol II). Late termination of mRNAs is performed by the CPF/CF complex and requires CTD-Ser2 phosphorylation. Early termination of shorter cryptic unstable transcripts (CUTs) and small nucleolar RNAs (snoRNAs) is preformed by the Nrd1 complex, and requires CTD-Ser5 phosphorylation. In this study, mutants of the different termination pathways were compared by genome-wide expression analysis. Surprisingly, the expression changes observed upon loss of the CTD-Ser2 kinase Ctk1 are more similar to loss of a subunit of the Ser5P binding Nrd1-complex, than to loss of Ser2P binding factors. Tiling array analysis of ctk1Δ reveals readthrough at several hundred sites, including snoRNAs, as reported previously, but also many cryptic unstable transcripts, stable untranslated transcripts (SUTs) and other transcripts. Surprisingly, neither loss of CTK1 nor a Pol II CTD-Ser2 substitution mutant results in a global defect in termination of mRNAs, indicating that Ser2P is not essential for proper termination of most mRNAs. At snoRNA, Nrd1 location is shifted downstream in ctk1∆, indicating defective release rather than recruitment of Nrd1. Weakening the interaction between Nrd1 and Pol II rescues the readthrough in ctk1∆, likely by facilitating Nrd1 release. The termination defect is kinase activity dependent, but cannot be completely explained by loss of CTD-Ser2 phosphorylation , a major substrate of Ctk1, suggesting the involvement of an additional substrate. Mutant alleles of the elongation factor Spt5 rescue ctk1∆-dependent readthrough, indicating a role for Spt5 in this process, perhaps as a substrate of Ctk1. The results show that Ctk1 is more intimately involved in termination of small non-coding RNAs than was previously assumed and lead to a model in which Ctk1 influences Spt5 activity to achieve this.

Project description:Transcription termination in Saccharomyces cerevisiae can be performed by at least two distinct pathways and is directed by the phosphorylation status of the carboxy-terminal domain (CTD) of RNA polymerase II (Pol II). Late termination of mRNAs is performed by the CPF/CF complex and requires CTD-Ser2 phosphorylation. Early termination of shorter cryptic unstable transcripts (CUTs) and small nucleolar RNAs (snoRNAs) is preformed by the Nrd1 complex, and requires CTD-Ser5 phosphorylation. In this study, mutants of the different termination pathways were compared by genome-wide expression analysis. Surprisingly, the expression changes observed upon loss of the CTD-Ser2 kinase Ctk1 are more similar to loss of a subunit of the Ser5P binding Nrd1-complex, than to loss of Ser2P binding factors. Tiling array analysis of ctk1Δ reveals readthrough at several hundred sites, including snoRNAs, as reported previously, but also many cryptic unstable transcripts, stable untranslated transcripts (SUTs) and other transcripts. Surprisingly, neither loss of CTK1 nor a Pol II CTD-Ser2 substitution mutant results in a global defect in termination of mRNAs, indicating that Ser2P is not essential for proper termination of most mRNAs. At snoRNA, Nrd1 location is shifted downstream in ctk1∆, indicating defective release rather than recruitment of Nrd1. Weakening the interaction between Nrd1 and Pol II rescues the readthrough in ctk1∆, likely by facilitating Nrd1 release. The termination defect is kinase activity dependent, but cannot be completely explained by loss of CTD-Ser2 phosphorylation , a major substrate of Ctk1, suggesting the involvement of an additional substrate. Mutant alleles of the elongation factor Spt5 rescue ctk1∆-dependent readthrough, indicating a role for Spt5 in this process, perhaps as a substrate of Ctk1. The results show that Ctk1 is more intimately involved in termination of small non-coding RNAs than was previously assumed and lead to a model in which Ctk1 influences Spt5 activity to achieve this. Two channel microarrays were used. RNA isolated from a large amount of wt yeast from a single culture was used as a common reference. This common reference was used in one of the channels for each hybridization and used in the statistical analysis to obtain an average expression-profile for each deletion mutant relative to the wt. Two independent cultures were hybridized on two separate microarrays. For the first hybridization the Cy5 (red) labeled cRNA from the deletion mutant is hybridized together with the Cy3 (green) labeled cRNA from the common reference. For the replicate hybridization, the labels are swapped. Each gene is represented twice on the microarray, resulting in four measurements per mutant. Using the Erlenmeyer growth protocol up to five deletion strains were grown on a single day. In the tecan platereader, up to eleven deletion strains could be grown on a single day. Wt cultures were grown parallel to the deletion mutants to assess day-to-day variance.

Project description:Spt6 is a multifunctional histone chaperone involved in the maintenance of chromatin structure during elongation by RNA polymerase II (Pol II). Spt6 has a tandem SH2 (tSH2) domain within its C-terminus that recognizes Pol II CTD peptides phosphorylated on Ser2, Ser5 or Try1 in vitro. Deleting the tSH2 domain, however, only has a partial effect on Spt6 occupancy in vivo, suggesting that more complex mechanisms are involved in the Spt6 recruitment. Our results show that the Ser2 kinases Bur1 and Ctk1, but not the Ser5 kinase Kin28, cooperate in recruiting Spt6, genome-wide. Interestingly, the Ser2 kinases promote the association of Spt6 in early transcribed regions and not toward the 3' end of genes, where phosphorylated Ser2 reaches its maximum level. Additionally, our results uncover an unexpected role for histone deacetylases (Rpd3 and Hos2) in promoting Spt6 interaction with elongating Pol II. Finally, our data suggest that phosphorylation of the Pol II CTD on Tyr1 promotes the association of Spt6 with the 3' end of transcribed genes, independently of Ser2 phosphorylation. Collectively, our results show that a complex network of interactions, involving the Spt6 tSH2 domain, CTD phosphorylation and histone deacetylases, coordinate the recruitment of Spt6 to transcribed genes in vivo. We examined the genome-wide distribution (using ChIP-chip) of Spt6. Spt6 occupancy was also assayed in mutants for CTD Serine 2 and Serine 5 kinases and in mutants for histone deacetylases. ChIPs were performed with a Myc-tagged version of Spt6. Most ChIPs (in Cy5) were hybridyzed against a control ChIP sample from an isogenic non-tagged strain (in Cy3). In the ChIP experiments with the spt6-202del mutant, non immunoprecipitated DNA (input) was used as the control. In addition to Spt6 ChIPs, the project includes RNAPII (Rpb3) ChIP-chip datasets, where an anti-Rpb3 antibody was used to ChIP RNAPII and non immunoprecipitated DNA (input) was used as the control. All ChIP-chip experiments were done in duplicates. Each microarray was normalized using the Lima Loess and replicates were combined using a weighted average method as previously described (Pokholok et al., 2005).

Dataset Information

Ctk1 + CTD mutants

Publications

The role of Ctk1 kinase in termination of small non-coding RNAs.

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