The interaction between the Spt6-tSH2 domain and Rpb1 affects multiple functions of RNA Polymerase II

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 of the Rpb1 subunit in a region linking the catalytic core and the heptad repeats at the C-terminal domain (CTD). This interaction contributes to generic localization of Spt6, but we show here that it also has gene-specific roles. Disrupting the interface affected transcription start site selection at a subset of genes whose expression is regulated by this choice, and this was accompanied by changes in the distinct pattern of Spt6 occupancy at these sites. Splicing efficiency was also impacted, as was apparent progression through introns that encode snoRNAs. Expression of genes that are particularly sensitive to efficient restoration of chromatin after transcription were affected, and a distinct role in maintaining +1 nucleosomes was identified, especially at ribosomal protein genes. The Spt6-tSH2:Rpb1 interface therefore has both genome-wide functions and local roles at subsets of genes where dynamic decisions regarding initiation, transcript processing, or termination are made. We propose that the Spt6-tSH2:Rpb1 interaction participates in coordinating appropriate responses to the varying local conditions encountered RNAPII at each gene, perhaps by modulating the elongation rate to allow reconfiguration of accessory factor activity or availability. Overall design: 21 samples (3 replicates each of 7 yeast strains) were grown to logarithmic phase (final OD ~0.8) in rich medium at 30° C. Cells were crosslinked with 1% formaldehyde for 20 minutes, collected by centrifugation, spheroplasted, digested with Micrococcal nuclease, then DNA was extracted.