RNA polymerase II carboxy-terminal domain phosphatase

grantor: University of TorontoThe form of RNA polymerase II (RNAPII) that binds preferentially to promoters is not extensively phosphorylated on the carboxy-terminal heptapeptide repeat domain (CTD) of its largest subunit. The CTD becomes phosphorylated during or shortly after initiation and elongating RNAPII generally has a phosphorylated CTD. Prior to or following transcriptional termination, dephosphorylation of the CTD presumably must occur to regenerate the hypophosphorylated form of RNAPII that is capable of reinitiating transcription. This thesis examines the function of the CTD phosphatase Fcp1p in the yeast 'Saccharomyces cerevisiae'. In chapter 2, it is shown that Fcp1 is an unusual eukaryotic protein phosphatase that is required for dephosphorylation of the CTD 'in vivo ' and for transcription by RNAPII 'in vivo'. These results suggest that Fcp1p is the founding member of a new class of protein phosphatases and acts as a general transcription factor 'in vivo'. In chapter 3, affinity chromatography is used to study the binding of Fcp1p to TFIIB and the RAP74 subunit of TFIIF. Fcp1p binds in a similar way to both of these factors. RAP74 and TFIIB have a short region of homology and amino acid changes in this region affect the binding to Fcp1p. The genes encoding RAP74 and Fcp1p interact 'in vivo'. Fcp1p can activate transcription when artificially tethered to a promoter and this effect is largely dependent on binding to RAP74. In chapter 4, it is shown that yeast strains with mutations in ' fcp1' grow much worse when the gene encoding the major CTD kinase Kin28p is also mutated. In contrast, inactivation of another CTD kinase encoded by the 'SRB10' gene suppresses the temperature-sensitivity and the sensitivity to certain cell cycle checkpoint inducing drugs of ' fcp1' mutant strains. These results therefore suggest that Fcp1p and Srb10p have opposing roles 'in vivo'. In chapter 5, analysis of the phosphorylation state of the CTD reveals that reduced Fcp1p activity results in a increased amount of the largest subunit of RNAPII but this subunit is not incorporated into functional enzyme and is largely degraded at a higher temperature.Ph.D