Howard Hughes Medical Institute; Program in Molecular Medicine; Program in Gene Function and Expression
Animals; Gene Products, tat; Globins; HIV-1; Hela Cells; Humans; Promoter Regions (Genetics); Recombinant Proteins; TATA-Binding Protein Associated Factors; TATA-Box Binding Protein; *Transcription, Genetic; Transfection; tat Gene Products, Human Immunodeficiency Virus
Life Sciences | Medicine and Health Sciences
The human immunodeficiency virus type I (HIV-1) transactivator protein Tat is an unusual transcriptional activator that is thought to act solely by promoting RNA polymerase II processivity. Here we study the mechanism of Tat action by analyzing transcription complex (TC) assembly in vivo using chromatin immunoprecipitation assays. We find, unexpectedly, that like typical activators Tat dramatically stimulates TC assembly. Surprisingly, however, the TC formed on the HIV-1 long terminal repeat is atypical and contains TATA-box-binding protein (TBP) but not TBP-associated factors (TAFs). Tat function involves direct interaction with the cellular cofactor positive transcription elongation factor b (P-TEFb). Artificial tethering of P-TEFb subunits to HIV-1 promoter DNA or nascent RNA indicates that P-TEFb is responsible for directing assembly of a TC containing TBP but not TAFs. On the basis of this finding, we identify P-TEFb-dependent cellular promoters that also recruit TBP in the absence of TAFs. Thus, in mammalian cells transcription of protein-coding genes involves alternative TCs that differ by the presence or absence of TAFs.
Rights and Permissions
Citation: PLoS Biol. 2005 Feb;3(2):e44. Epub 2005 Feb 8. Link to article on publisher's site