TY - JOUR TI - The AFF4 scaffold binds human P-TEFb adjacent to HIV Tat AU - Schulze-Gahmen, Ursula AU - Upton, Heather AU - Birnberg, Andrew AU - Bao, Katherine AU - Chou, Seemay AU - Krogan, Nevan J AU - Zhou, Qiang AU - Alber, Tom A2 - Sundquist, Wes VL - 2 PY - 2013 DA - 2013/03/05 SP - e00327 C1 - eLife 2013;2:e00327 DO - 10.7554/eLife.00327 UR - https://doi.org/10.7554/eLife.00327 AB - Human positive transcription elongation factor b (P-TEFb) phosphorylates RNA polymerase II and regulatory proteins to trigger elongation of many gene transcripts. The HIV-1 Tat protein selectively recruits P-TEFb as part of a super elongation complex (SEC) organized on a flexible AFF1 or AFF4 scaffold. To understand this specificity and determine if scaffold binding alters P-TEFb conformation, we determined the structure of a tripartite complex containing the recognition regions of P-TEFb and AFF4. AFF4 meanders over the surface of the P-TEFb cyclin T1 (CycT1) subunit but makes no stable contacts with the CDK9 kinase subunit. Interface mutations reduced CycT1 binding and AFF4-dependent transcription. AFF4 is positioned to make unexpected direct contacts with HIV Tat, and Tat enhances P-TEFb affinity for AFF4. These studies define the mechanism of scaffold recognition by P-TEFb and reveal an unanticipated intersubunit pocket on the AFF4 SEC that potentially represents a target for therapeutic intervention against HIV/AIDS. KW - transcription elongation KW - super elongation complex KW - SEC KW - intrinsically disordered protein JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -