1st National Conference Human Retroviruses and Related Infections Washington, DC - December 12-16, 1993

Natl Conf Hum Retrovir Relat Infect 1993 Dec 12-16;1: (abstract no. 20)

Herrmann CH, Rhim H, Echetebu CO, Rice AP
Baylor College of Medicine, Houston, TX 77030 USA

The Tat proteins of human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) stimulate viral gene expression by binding to the TAR RNA element located at the 5' end of all nascent viral transcripts. The RNA binding domain of Tat proteins binds directly to TAR RNA, while the activation domain stimulates transcription by an unknown mechanism that presumably utilizes a cellular factor. The result of Tat action is more processive transcriptional elongation and in some experimental systems an additional increase in transcriptional initiation.

Using an in vitro kinase assay, we have found that the HIV-2 Tat protein and the activation domain of the HIV-1 Tat protein specifically bind to a cellular protein kinase present in HeLa cell nuclear extracts. Point mutations in Tat that abolish transactivation activity in vivo abrogate the ability of the mutants to bind to the kinase in vitro. Thus, this protein kinase that binds to Tat in vitro is specific for a functional activation domain of Tat. Additionally, we have found that the Tat protein of HIV-2, but not HIV-1, serves as a substrate of the kinase in vitro and is phosphorylated on serine and threonine residues. A 42 kDa protein, which may be a subunit of the kinase, is also phosphorylated in the in vitro reaction. Consistent with the in vitro results, the Tat protein of HIV-2 is phosphorylated in vivo and can also be co-immunoprecipitated with a kinase activity in HIV-2 Tat-transfected cells. Our results suggest that a cellular serine/threonine kinase may act as a mediator of Tat function. We are currently purifying this kinase and further characterizing its biochemical properties.

Keywords: AIDS Vaccines, Gene Products, tat, Genes, tat, HIV, HIV Long Terminal Repeat, HIV-1, HIV-2, Hela Cells, Humans, In Vitro, Protein Kinases, Protein-Serine-Threonine Kinases, Trans-Activation (Genetics), Transcription, Genetic, genetics

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1993-12-12
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