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Comparative Study
. 1989 Oct 20;59(2):283-92.
doi: 10.1016/0092-8674(89)90290-0.

HIV-1 Tat protein increases transcriptional initiation and stabilizes elongation

M F Laspia  1 , A P Rice, M B Mathews
Affiliations
Comparative Study

HIV-1 Tat protein increases transcriptional initiation and stabilizes elongation

M F Laspia et al. Cell. .

Abstract

We studied regulation of human immunodeficiency virus-1 (HIV-1) transcription by Tat and, for comparative purposes, by the adenovirus E1A protein. These two trans-activators exerted different effects. Two classes of HIV-1-promoted cytoplasmic RNA were detected, one class corresponding to full-length transcripts and the other to transcripts ending 55 and 59 nucleotides from the transcription start. Tat increased the level of the full-length class only, whereas E1A increased the levels of both classes of RNA. We also measured the effects of Tat and E1A on RNA synthesis rates. Without trans-activators, HIV-1-directed transcription was relatively weak and exhibited a marked polarity. Both Tat and E1A dramatically increased promoter-proximal transcription, while only Tat suppressed transcriptional polarity. Mutations in the TAR element did not influence basal transcription rates or the response to E1A, but eliminated trans-activation by Tat. We propose that Tat acts through TAR to increase initiation complex formation on the HIV-1 promoter and to stabilize complexes during elongation.

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