| Autor: |
Parua PK; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029-6574, USA., Kalan S; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029-6574, USA., Benjamin B; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029-6574, USA., Sansó M; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029-6574, USA., Fisher RP; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, 10029-6574, USA. Robert.fisher@mssm.edu. |
| Abstrakt: |
Reversible phosphorylation of Pol II and accessory factors helps order the transcription cycle. Here, we define two kinase-phosphatase switches that operate at different points in human transcription. Cdk9/cyclin T1 (P-TEFb) catalyzes inhibitory phosphorylation of PP1 and PP4 complexes that localize to 3' and 5' ends of genes, respectively, and have overlapping but distinct specificities for Cdk9-dependent phosphorylations of Spt5, a factor instrumental in promoter-proximal pausing and elongation-rate control. PP1 dephosphorylates an Spt5 carboxy-terminal repeat (CTR), but not Spt5-Ser666, a site between Kyrpides-Ouzounis-Woese (KOW) motifs 4 and 5, whereas PP4 can target both sites. In vivo, Spt5-CTR phosphorylation decreases as transcription complexes pass the cleavage and polyadenylation signal (CPS) and increases upon PP1 depletion, consistent with a PP1 function in termination first uncovered in yeast. Depletion of PP4-complex subunits increases phosphorylation of both Ser666 and the CTR, and promotes redistribution of promoter-proximally paused Pol II into gene bodies. These results suggest that switches comprising Cdk9 and either PP4 or PP1 govern pause release and the elongation-termination transition, respectively. |
