AFF4 binding to Tat-P-TEFb indirectly stimulates TAR recognition of super elongation complexes at the HIV promoter.
Superelongation complexes (SECs) are essential for transcription elongation of many human genes, including the integrated HIV-1 genome. At the HIV-1 promoter, the viral Tat protein binds simultaneously to the nascent TAR RNA and the CycT1 subunit of the P-TEFb kinase in a SEC. To understand the preferential recruitment of SECs by Tat and TAR, we determined the crystal structure of a quaternary complex containing Tat, P-TEFb, and the SEC scaffold, AFF4. Tat and AFF4 fold on the surface of CycT1 and interact directly. Interface mutations in the AFF4 homolog AFF1 reduced Tat-AFF1 affinity in vivo and Tat-dependent transcription from the HIV promoter. AFF4 binding in the presence of Tat partially orders the CycT1 Tat-TAR recognition motif and increases the affinity of Tat-P-TEFb for TAR 30-fold. These studies indicate that AFF4 acts as a two-step filter to increase the selectivity of Tat and TAR for SECs over P-TEFb alone.DOI: http://dx.doi.org/10.7554/eLife.02375.001.
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States uschulze-gahmen@berkeley.edu.
Ursula
U
Schulze-Gahmen
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
Huasong
H
Lu
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
Qiang
Q
Zhou
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States California Institute for Quantitative Biosciences, QB3, University of California, Berkeley, Berkeley, United States.
Tom
T
Alber
D015967:Gene Expression Regulation, Viral; D015696:Gene Products, tat / Q000235:genetics* / Q000378:metabolism; D016679:Genome, Viral; D016325:HIV Long Terminal Repeat / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D042925:Positive Transcriptional Elongation Factor B / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D012367:RNA, Viral / Q000235:genetics / Q000302:isolation & purification; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism
C471348:AFF4 protein, human; D015696:Gene Products, tat; D012367:RNA, Viral; D012097:Repressor Proteins; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins; D042925:Positive Transcriptional Elongation Factor B
Tat-AFF4-CycT1 interface; Tat-TAR recognition motif; crystal structure; transcriptional elongation