A kinase–cyclin pair in the RNA polymerase II holoenzyme

Abstract

THE RNA polymerase II holoenzyme consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as SRB proteins^1,2. The genes encoding SRB proteins were isolated as suppressors of mutations in the RNA polymerase II carboxy-terminal domain (CTD)^3,4. The CTD and SRB proteins have been implicated in the response to transcriptional regulators^1–11. We report here the isolation of two new SRB genes, SRB10 and SRB11, which encode kinase- and cyclin-like proteins, respectively. Genetic and biochemical evidence indicates that the SRB 10 and SRB 11 proteins form a kinase–cyclin pair in the holoenzyme. The SRB10/11 kinase is essential for a normal transcriptional response to galactose induction in vivo. Holoenzymes lacking SRB 10/11 kinase function are strikingly deficient in CTD phosphory lation. Although defects in the kinase substantially affect transcription in vivo, purified holoenzymes lacking SRB10/11 kinase function do not show defects in definedin vitro transcription systems, suggesting that the factors necessary to elicit the regulatory role of the SRB10/11 kinase are missing in these systems. These results indicate that the SRB 10/11 kinase is involved in CTD phosphorv lation and suggest that this modification has a role in the response to transcriptional regulators in vivo.