The HIV-1 Tat protein activates transcription from an upstream DNA-binding site: implications for Tat function.
The Tat protein of human immunodeficiency virus type 1 (HIV-1) activates transcription following binding to nascent trans-activation response (TAR) RNA downstream of the transcription start site. Because Tat functions when bound to RNA, and in a position-dependent manner, it has been proposed that Tat works by a novel mechanism. Here, we perform a series of protein fusion experiments that reveal striking similarities between Tat and conventional cellular activators. Most significantly, we demonstrate that Tat can function when bound to upstream promoter DNA. This activity depends on a region within Tat that is also required for Tat to function when bound to TAR RNA. In contrast, the arginine-rich region of Tat, which is required for binding to TAR RNA, is dispensable for the function of DNA-bound Tat. When bound either to RNA or DNA Tat activity requires cooperation with promoter-bound cellular transcription factors. Finally, we show that Tat and a strong acidic activator stimulate transcription to comparable levels. On the basis of these and other results we suggest that Tat and acidic activators act on a similar step in the transcription process.
Southgate
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Program in Molecular Medicine, University of Massachusetts Medical Center, Worcester 01605.
Green
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D001483:Base Sequence; D004252:DNA Mutational Analysis; D004279:DNA, Viral / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D015696:Gene Products, tat / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D014760:Viral Fusion Proteins / Q000502:physiology; D054322:tat Gene Products, Human Immunodeficiency Virus
D004279:DNA, Viral; C064255:GAL4 (1-147) protein, S cerevisiae; D015696:Gene Products, tat; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D014760:Viral Fusion Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus