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Molecular and Cellular Biology, May 2000, p. 2970-2983, Vol. 20, No. 9
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Domains in the SPT5 Protein That Modulate Its Transcriptional Regulatory Properties

Dmitri Ivanov, Youn Tae Kwak, Jun Guo, and Richard B. Gaynor*

Division of Hematology-Oncology, Department of Medicine, Harold Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas 75235-8594

Received 13 December 1999/Returned for modification 21 January 2000/Accepted 2 February 2000

SPT5 and its binding partner SPT4 regulate transcriptional elongation by RNA polymerase II. SPT4 and SPT5 are involved in both 5,6-dichloro-1-beta -D-ribofuranosylbenzimidazole (DRB)-mediated transcriptional inhibition and the activation of transcriptional elongation by the human immunodeficiency virus type 1 (HIV-1) Tat protein. Recent data suggest that P-TEFb, which is composed of CDK9 and cyclin T1, is also critical in regulating transcriptional elongation by SPT4 and SPT5. In this study, we analyze the domains of SPT5 that regulate transcriptional elongation in the presence of either DRB or the HIV-1 Tat protein. We demonstrate that SPT5 domains that bind SPT4 and RNA polymerase II, in addition to a region in the C terminus of SPT5 that contains multiple heptad repeats and is designated CTR1, are critical for in vitro transcriptional repression by DRB and activation by the Tat protein. Furthermore, the SPT5 CTR1 domain is a substrate for P-TEFb phosphorylation. These results suggest that C-terminal repeats in SPT5, like those in the RNA polymerase II C-terminal domain, are sites for P-TEFb phosphorylation and function in modulating its transcriptional elongation properties.

* Corresponding author. Mailing address: Division of Hematology-Oncology, Department of Medicine, U.T. Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235-8594. Phone: (214) 648-7570. Fax: (214) 648-8862. E-mail: gaynor{at}utsw.swmed.edu.

Molecular and Cellular Biology, May 2000, p. 2970-2983, Vol. 20, No. 9
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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