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The Spt6-tSH2 domain coordinates functional transitions of the RNA Polymerase II CTD during initiation and elongation.

ABSTRACT: The conserved transcription elongation factor Spt6 makes several contacts with the RNA Polymerase II (RNAPII) complex, including a high-affinity interaction between the Spt6 tandem SH2 domain (Spt6-tSH2) and phosphorylated residues in Rpb1 in a region between the catalytic core and the heptad repeats of its C-terminal domain (CTD). This interaction contributes to the global occupancy of Spt6 within transcription units, suggesting that it has a general role in tethering Spt6 to the elongation complex. However, we show here that disrupting this binding caused increases in some transcripts, revealing specific functional roles in regulating the expression of subsets of genes. These included loci whose regulation involves differential transcription start site selection, early termination of transcription, or efficient restoration of chromatin integrity after transcription. Loss of this interaction also caused a defect in splicing, and apparent pausing of RNAPII progression in regions requiring more complex processing of excised introns. The results support a global role for the Spt6-tSH2:Rpb1 interaction as one of several means of stabilizing the association of Spt6 with RNAPII, but they also reveal local functions at specific sites, especially those where dynamic decisions regarding initiation or termination are made, or where changes in the configuration of associated factors occur. We therefore propose that the Spt6-tSH2:Rpb1 interaction can provide a conduit for communication between RNAPII and the elongation factor function of Spt6, or with other factors associated with the Rpb1 CTD, supporting appropriate elongation through challenging templates and efficient co-transcriptional processing.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE174427 | GEO | 2021/12/20

REPOSITORIES: GEO

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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).

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The Spt6-tSH2 domain coordinates functional transitions of the RNA Polymerase II CTD during initiation and elongation.

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