HIV-1 Tat stimulates transcription complex assembly through recruitment of TBP in the absence of TAFs.
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.
Raha
Tamal
T
Howard Hughes Medical Institute, Program in Gene Function, University of Massachusetts Medical School, Worcester, USA.
Cheng
S W Grace
SW
Green
Michael R
MR
D000818:Animals; D015696:Gene Products, tat / Q000378:metabolism*; D005914:Globins / Q000235:genetics; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D035381:TATA-Binding Protein Associated Factors / Q000235:genetics / Q000378:metabolism*; D035181:TATA-Box Binding Protein / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D011994:Recombinant Proteins; D035381:TATA-Binding Protein Associated Factors; D035181:TATA-Box Binding Protein; D054322:tat Gene Products, Human Immunodeficiency Virus; D005914:Globins
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