Making Yeast Horny

Science Signaling  29 Jun 2010:
Vol. 3, Issue 128, pp. ec192
DOI: 10.1126/scisignal.3128ec192

Fission yeast typically divide asexually unless starved for nitrogen, which triggers a switch to sexual reproduction. Sexual reproduction in Schizosaccharomyces pombe is initiated through the transcriptional induction of the Ste11 transcription factor, which is the master regulator of mating and meiosis. In a genome-wide analysis of the interaction of the RNA polymerase II (RNA PolII) kinases (Mcs6, Cdk9, and Lsk1) and specific phosphorylated forms of RNA PolII, Coudreuse et al. found an unexpected chromatin distribution of RNA PolII phosphorylated at the Ser2 sites in its C-terminal domain (CTD) heptad repeat (YSPTSPS) and ultimately determined that the RNA PolII kinase Lsk1 and this Ser2-phosphorylated RNA PolII (S2P) were specifically required for ste11 induction. Analysis of drug-sensitive mutants (Msc6 and Cdk9) or genetic knockout strains (Lsk1) and in vitro kinase assays with alanine point mutants of the CTD showed that Lsk1 only phosphorylated the Ser2 site, whereas Mcs6 and Cdk9 phosphorylated both the Ser2 and the Ser5 site. Genome-wide occupancy analysis of vegetative cells showed that Ser5-phosphorylated PolII (S5P), Mcs6, and Cdk9 were correlated and broadly distributed, whereas S2P and Lsk1 had a more restricted pattern of chromatin association. The distribution of S5P or S2P and individual PolII kinases showed distinct patterns with respect to where along the gene they were present: Mcs6 showed a peak at promoters, and Cdk9 showed a bimodal distribution with a peak at the beginning of the coding region and a peak at the 3'-untranslated region. S2P and Lsk1 exhibited distinct patterns at different genes, with some showing enrichment at the 5'-untranslated region and some enrichment at the 3'-untranslated region. Detailed analysis of ste11, which showed 5'-untranslated region enrichment, revealed that recruitment of the RNA PolII was dependent on S2P and Lsk1 and ste11 mRNA failed to increase in response to nitrogen starvation in cells carrying S2P-deficient RNA PolII or lacking Lsk1. These S2P-deficient or Lsk1-deficient cells also failed to undergo mating and meiosis; sterility of the Lsk1-deficient strain was rescued by forced expression of ste11 from a plasmid with the adh1 promoter, which is not regulated by S2P and Lsk1. Thus, the cyclin-dependent kinase Lsk1 specifically phosphorylates RNA PolII at the 5'-untranslated region of ste11 to allow gene-specific transcription.

D. Coudreuse, H. van Bakel, M. Dewez, J. Soutourina, T. Parnell, J. Vandenhaute, B. Cairns, M. Werner, D. Hermand, A gene-specific requirement of RNA polymerase II CTD phosphorylation for sexual differentiation in S. pombe. Curr. Biol. 20, 1053–1064 (2010). [Online Journal]