A kinase-cyclin pair in the RNA polymerase II holoenzyme.
Liao, Sha-Mei; Zhang, Jianhua; Jeffery, Douglas A.; Koleske, Anthony J.; Thompson, Craig M.; Chao, David M.; Viljoen, Marinda; van Vuuren, Hendrik J. J.; Young, Richard A.
[Letter] Nature. 374(6518):193-196, March 9, 1995.

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The RNA polymerase II holoenzyme consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as SRB proteins *RF 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 SRB10 and SRB11 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 SRB10/11 kinase function are strikingly deficient in CTD phosphorylation. Although defects in the kinase substantially affect transcription in vivo, purified holoenzymes lacking SRB10/11 kinase function do not show defects in defined in 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 SRB10/11 kinase is involved in CTD phosphorylation and suggest that this modification has a role in the response to transcriptional regulators in vivo.

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