Yeast carboxyl-terminal domain kinase I positively and negatively regulates RNA polymerase II carboxyl-terminal domain phosphorylation

Monoclonal antibodies that recognize specific carboxyl-terminal domain (CTD ) phosphoepitopes were used to examine CTD phosphorylation in yeast cells l acking carboxyl-terminal domain kinase I (CTDK-I). We show that deletion of the kinase subunit CTK1 results in an increase in phosphorylation of serin e in position 5 (Ser(5)) of the CTD repeat (Tyr(1)-Ser(2)-Pro(3)-Thr(4)-Ser (5)-Pro(6)-Ser(7)) during logarithmic growth. This result indicates that CT DK-I negatively regulates CTD Ser5 phosphorylation. We also show that CTK1 deletion (cth1 Delta) eliminates the transient increase in CTD serine 2 (Se r(2)) phosphorylation observed during the diauxic shift. This result sugges ts that CTDK-I may play a direct role in phosphorylating CTD Ser(2) in resp onse to nutrient depletion. Northern blot analysis was used to show that ge nes normally induced during the diauxic shift are not properly induced in a ctk1 Delta strain. Glycogen synthase (GSY2) and cytosolic catalase (CTT1) mRNA levels increase about 10-fold in wild-type cells, but this increase is not observed in ctk1 Delta cells suggesting that increased message levels may require Ser(2) phosphorylation. Heat shock also induces Ser(2) phosphor ylation, but we show here that this change in CTD modification and an accom panying induction of heat shock gene expression is independent of CTDK-I. T he observation that SSA3/SSA4 expression is increased in ctk1 Delta cells g rown at normal temperature suggests a possible role for CTDK-I in transcrip tion repression. We discuss several possible positive and negative roles fo r CTDK-I in regulating CTD phosphorylation and gene expression.