Investigating the role of Dis2 phosphatase in RNA Polymerase II transcription termination in fission yeast

The end of the RNA polymerase II (Pol II) transcription cycle is a tightly regulated process that requires: (i) dissociation of elongation factors, (ii) recruitment of the 3' end processing machinery that is essential for premRNA cleavage and polyadenylation, and (iii) association of termination factors to dislodge Pol II from the DNA template. A characteristic feature of termination factors is that they directly interact with the phosphorylated C-terminal domain (CTD) of the largest subunit of Pol II (Rpb1). The CTD consists of heptad repeats (Y1S2P3T4S5P6S7) where Tyr1, Ser2, Ser5, Ser7 and Thr4 can be reversibly phosphorylated during the transcription cycle. The work presented here reveals that Thr4 phosphorylation levels are enriched at the 3' ends of protein-coding genes in fission yeast and identies Dis2 as a Pol II-CTD phosphatase that dephosphorylates Thr4 both in vitro and in vivo. Dis2 activity is required for Thr4 dephosphorylation at the polyadenylation site, for recruitment of termination factors Pcf11, Rhn1 and Seb1 and for normal Pol II termination. Interestingly, Seb1 cotranscriptional recruitment is shown to be dependent not on Dis2 activity on CTD but on its ability to dephosphorylate the elongation factor Spt5, suggesting that Dis2 regulates the elongation-to-termination transition by targeting multiple substrates.