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Journal of Virology, November 2008, p. 10591-10599, Vol. 82, No. 21
0022-538X/08/$08.00+0 doi:10.1128/JVI.01242-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Marjorie B. Kovler Viral Oncology Laboratories, The University of Chicago, 910 East 58th Street, Chicago, Illinois 60637
Received 15 June 2008/ Accepted 19 August 2008
ICP22 is a multifunctional herpes simplex virus 1 (HSV-1) regulatory protein that regulates the accumulation of a subset of late (
2) proteins exemplified by UL38, UL41, and US11. ICP22 binds the cyclin-dependent kinase 9 (cdk9) but not cdk7, and this complex in conjunction with viral protein kinases phosphorylates the carboxyl terminus of RNA polymerase II (Pol II) in vitro. The primary function of cdk9 and its partners, the cyclin T variants, is in the elongation of RNA transcripts, although functions related to the initiation and processing of transcripts have also been reported. We report two series of experiments designed to probe the role of cdk9 in infected cells. In the first, infected cells were treated with 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole (DRB), a specific inhibitor of cdk9. In cells treated with DRB, the major effect was in the accumulation of viral RNAs and proteins regulated by ICP22. The accumulation of
, β, or
proteins not regulated by ICP22 was not affected by the drug. The results obtained with DRB were duplicated in cells transfected with small interfering RNA (siRNA) targeting cdk9 mRNAs. Interestingly, DRB and siRNA reduced the levels of ICP22 but not those of other
gene products. In addition, cdk9 and ICP22 appeared to colocalize with RNA Pol II in wild-type-virus-infected cells but not in
UL13-infected cells. We conclude that cdk9 plays a critical role in the optimization of expression of genes regulated by ICP22 and that one function of cdk9 in HSV-1-infected cells may be to bring ICP22 into the RNA Pol II transcriptional complex.
Published ahead of print on 27 August 2008.
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