Cyclin K Functions as a CDK9 Regulatory Subunit and Participates in RNA Polymerase II Transcription*
- From the Department of Biology, Tularik Inc., South San Francisco, California 92080 and the §Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242
Abstract
Important progress in the understanding of elongation control by RNA polymerase II (RNAPII) has come from the recent identification of the positive transcription elongation factor b (P-TEFb) and the demonstration that this factor is a protein kinase that phosphorylates the carboxyl-terminal domain (CTD) of the RNAPII largest subunit. The P-TEFb complex isolated from mammalian cells contains a catalytic subunit (CDK9), a cyclin subunit (cyclin T1 or cyclin T2), and additional, yet unidentified, polypeptides of unknown function. To identify additional factors involved in P-TEFb function we performed a yeast two-hybrid screen using CDK9 as bait and found that cyclin K interacts with CDK9 in vivo. Biochemical analyses indicate that cyclin K functions as a regulatory subunit of CDK9. The CDK9-cyclin K complex phosphorylated the CTD of RNAPII and functionally substituted for P-TEFb comprised of CDK9 and cyclin T in in vitro transcription reactions.
Footnotes
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↵* This work was supported in part by National Institutes of Health Grants GM 35500 and A143691.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Present address: Gen-Probe Inc., San Diego, CA 92121.
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↵¶ Present address: Howard Hughes Medical Institute, Dept. of Pathology, Harvard Medical School, Boston, MA 02115.
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↵‖ To whom correspondence should be addressed: Present address: Dept. of Antiviral Research, Merck Research Laboratories, West Point, PA 19446. Tel.: 215-652-6384; Fax: 215-652-0994.
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↵2 O. Flores, unpublished observations.
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↵3 T. J. Fu and O. Flores, unpublished results.
- Abbreviations:
- RNAPII
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RNA polymerase II
- P-TEFb
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positive transcription elongation factor b
- DRB
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5,6-dichloro-1-β-d-ribofuranosylbenzimidazole
- CTD
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carboxyl-terminal domain
- HIV
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human immunodeficiency virus
- BME
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β-mercaptoethanol
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- Received August 13, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
