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Molecular and Cellular Biology, March 2002, p. 1288-1297, Vol. 22, No. 5
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.5.1288-1297.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Kin28 Is Found within TFIIH and a Kin28-Ccl1-Tfb3 Trimer Complex with Differential Sensitivities to T-Loop Phosphorylation

Michael-Christopher Keogh,1 Eun-Jung Cho,1,2 Vladimir Podolny,1 and Stephen Buratowski1*

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115,1 and Department of Biochemistry and Molecular Biology, College of Pharmacy, Sungkyunkwan University, Suwon, Korea2

Received 4 October 2001/ Returned for modification 14 November 2001/ Accepted 30 November 2001

Basal transcription factor TFIIH phosphorylates the RNA polymerase II (RNApII) carboxy-terminal domain (CTD) within the transcription initiation complex. The catalytic kinase subunit of TFIIH is a member of the cyclin-dependent kinase (Cdk) family, designated Kin28 in Saccharomyces cerevisiae and Cdk7 in higher eukaryotes. Together with TFIIH subunits cyclin H and Mat1, Cdk7 kinase is also found in a trimer complex known as Cdk activating kinase (CAK). A yeast trimer complex has not previously been identified, although a Kin28-Ccl1 dimer called TFIIK has been isolated as a breakdown product of TFIIH. Here we show that a trimeric complex of Kin28-Ccl1-Tfb3 exists in yeast extracts. Several Kin28 point mutants that are defective in CTD phosphorylation were created. Consistent with earlier studies, these mutants have no transcriptional defect in vitro. Like other Cdks, Kin28 is activated by phosphorylation on T162 of the T loop. Kin28 T162 mutants have no growth defects alone but do demonstrate synthetic phenotypes when combined with mutant versions of the cyclin partner, Ccl1. Surprisingly, these phosphorylation site mutants appear to destabilize the association of the cyclin subunit within the context of TFIIH but not within the trimer complex.

* Corresponding author. Mailing address: Dept of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115. Phone: (617) 432-0696. Fax: (617) 738-0516. E-mail: steveb{at}hms.harvard.edu.

Molecular and Cellular Biology, March 2002, p. 1288-1297, Vol. 22, No. 5
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.5.1288-1297.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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