TY - JOUR TI - AFF4 binding to Tat-P-TEFb indirectly stimulates TAR recognition of super elongation complexes at the HIV promoter AU - Schulze-Gahmen, Ursula AU - Lu, Huasong AU - Zhou, Qiang AU - Alber, Tom A2 - Sundquist, Wesley VL - 3 PY - 2014 DA - 2014/04/24 SP - e02375 C1 - eLife 2014;3:e02375 DO - 10.7554/eLife.02375 UR - https://doi.org/10.7554/eLife.02375 AB - 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. KW - crystal structure KW - transcriptional elongation KW - Tat-AFF4-CycT1 interface KW - Tat-TAR recognition motif JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -