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Journal of Virology, June 2009, p. 5904-5917, Vol. 83, No. 11
0022-538X/09/$08.00+0     doi:10.1128/JVI.02651-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Recruitment of cdk9 to the Immediate-Early Viral Transcriptosomes during Human Cytomegalovirus Infection Requires Efficient Binding to Cyclin T1, a Threshold Level of IE2 86, and Active Transcription{triangledown}

Anokhi J. Kapasi, Charles L. Clark, Karen Tran, and Deborah H. Spector*

Department of Cellular and Molecular Medicine and School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093-0712

Received 23 December 2008/ Accepted 6 March 2009

Human cytomegalovirus (HCMV) infection results in the formation of nuclear viral transcriptosomes, which are sites dedicated to viral immediate-early (IE) transcription. At IE times of the infection, viral and cellular factors, including several components of transcription such as cyclin-dependent kinase 9 (cdk9), localize at these sites. To determine the mechanism and requirements of specific recruitment of cdk9 to the viral transcriptosomes, infection in the presence of inhibitor drugs and infection of cell lines expressing exogenous mutant cdk9 were performed. We found that cdk9 localization to the viral transcriptosomes requires de novo protein synthesis. In addition, active transcription is required for recruitment and maintenance of cdk9 at the viral transcriptosomes. In cells infected with a recombinant IE2 HCMV (IE2 86 {Delta}SX virus) in which IE2 gene expression is greatly reduced, cdk9 localization at the transcriptosome is delayed and corresponds to the kinetics of accumulation of the IE2 protein at these sites. Infection in the presence of the cdk9 inhibitors Flavopiridol and DRB (5,6-dichloro-1-β-D-ribofuranosylbenzimidazole) allowed cdk9 localization to the viral transcriptosomes. A kinase-inactive cdk9 (D167N) expressed during the infection also localizes to the viral transcriptosomes, indicating that kinase activity of cdk9 is not a requirement for its localization to the sites of IE transcription. Exogenous expression of additional cdk9 mutants indicates that binding of Brd4 to the cdk9 complex is not required but that efficient binding to cyclin T1 is essential.

* Corresponding author. Mailing address: Skaggs School of Pharmacy and Pharmaceutical Sciences, Room 3254, Mail Code 0712, 9500 Gilman Drive, University of California, San Diego, La Jolla, CA 92093-0712. Phone: (858) 822-4003. Fax: (858) 534-6083. E-mail: dspector{at}ucsd.edu

{triangledown} Published ahead of print on 18 March 2009.

Journal of Virology, June 2009, p. 5904-5917, Vol. 83, No. 11
0022-538X/09/$08.00+0     doi:10.1128/JVI.02651-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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