HIV-1 Tat protein promotes formation of more-processive elongation complexes.
The Tat protein of HIV-1 trans-activates transcription in vitro in a cell-free extract of HeLa nuclei. Quantitative analysis of the efficiency of elongation revealed that a majority of the elongation complexes generated by the HIV-1 promoter were not highly processive and terminated within the first 500 nucleotides. Tat trans-activation of transcription from the HIV-1 promoter resulted from an increase in processive character of the elongation complexes. More specifically, the analysis suggests that there exist two classes of elongation complexes initiating from the HIV promoter: a less-processive form and a more-processive form. Addition of purified Tat protein was found to increase the abundance of the more-processive class of elongation complex. The purine nucleoside analog, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibits transcription in this reaction by decreasing the efficiency of elongation. Surprisingly, stimulation of transcription elongation by Tat was preferentially inhibited by the addition of DRB.
Marciniak
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RA
Center for Cancer Research, Massachusetts Institute of Technology, Cambridge 02139.
Sharp
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PA
D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D015696:Gene Products, tat / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012367:RNA, Viral / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D012367:RNA, Viral; D054322:tat Gene Products, Human Immunodeficiency Virus; D004004:Dichlororibofuranosylbenzimidazole