The AFF4 scaffold binds human P-TEFb adjacent to HIV Tat

• Main Authors: Ursula Schulze-Gahmen, Heather Upton, Andrew Birnberg, Katherine Bao, Seemay Chou, Nevan J Krogan, Qiang Zhou, Tom Alber
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2013-03-01
• Series: eLife
• Subjects: transcription elongation; super elongation complex; SEC; intrinsically disordered protein
• Online Access: https://elifesciences.org/articles/00327

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.