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HIV-1 Vif hijacks a cellular ubiquitin ligase complex to degrade antiviral APOBEC3 enzymes and PP2A phosphatase regulators (PPP2R5A-E). APOBEC3 counteraction is essential for viral pathogenesis. However, Vif also functions through an unknown mechanism to induce G2 cell cycle arrest. Here, deep mutagenesis is used to define the Vif surface required for PPP2R5 degradation and isolate a panel of separation-of-function mutants (PPP2R5 degradation-deficient and APOBEC3G degradation-proficient). Functional studies with Vif and PPP2R5 mutants were combined to demonstrate that PPP2R5 is, in fact, the target Vif degrades to induce G2 arrest. Pharmacologic and genetic approaches show that direct modulation of PP2A function or depletion of specific PPP2R5 proteins causes an indistinguishable arrest phenotype. Vif function in the cell cycle checkpoint is present in common HIV-1 subtypes worldwide and likely advantageous for viral pathogenesis., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

The transition from transcription initiation to elongation at promoters of primary response genes (PRGs) in metazoan cells is controlled by inducible transcription factors, which utilize P-TEFb to phosphorylate RNA polymerase II (Pol II) in response to stimuli. Prior to stimulation, a fraction of P-TEFb is recruited to promoter-proximal regions in a catalytically inactive state bound to the 7SK small nuclear ribonucleoprotein (snRNP) complex. However, it remains unclear how and why the 7SK snRNP is assembled at these sites. Here we report that the transcriptional regulator KAP1 continuously tethers the 7SK snRNP to PRG promoters to facilitate P-TEFb recruitment and productive elongation in response to stimulation. Remarkably, besides PRGs, genome-wide studies revealed that KAP1 and 7SK snRNP co-occupy most promoter-proximal regions containing paused Pol II. Collectively, we provide evidence of an unprecedented mechanism controlling 7SK snRNP delivery to promoter-proximal regions to facilitate "on-site" P-TEFb activation and Pol II elongation., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The transition from transcription initiation into elongation is controlled by transcription factors, which recruit positive transcription elongation factor b (P-TEFb) to promoters to phosphorylate RNA polymerase II. A fraction of P-TEFb is recruited as part of the inhibitory 7SK small nuclear ribonucleoprotein particle (snRNP), which inactivates the kinase and prevents elongation. However, it is unclear how P-TEFb is captured from the promoter-bound 7SK snRNP to activate elongation. Here, we describe a mechanism by which transcription factors mediate the enzymatic release of P-TEFb from the 7SK snRNP at promoters to trigger activation in a gene-specific manner. We demonstrate that Tat recruits PPM1G/PP2Cγ to locally disassemble P-TEFb from the 7SK snRNP at the HIV promoter via dephosphorylation of the kinase T loop. Similar to Tat, nuclear factor (NF)-κB recruits PPM1G in a stimulus-dependent manner to activate elongation at inflammatory-responsive genes. Recruitment of PPM1G to promoter-assembled 7SK snRNP provides a paradigm for rapid gene activation through transcriptional pause release., (Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.)