FIG. 6.

MMTR inhibits CAK-mediated RNA polymerase II CTD phosphorylation. (A) 293T cells were cotransfected with Flag-CDK7, Flag-cyclin H, and Flag-MAT1 expression vectors. Cell extracts were immunoprecipitated with an HA or Flag antibody, and each precipitate was incubated with kinase reaction buffer with recombinant GST-CTD as a substrate. Phosphorylation of GST-CTD was visualized by SDS-PAGE, followed by autoradiography. (B) Kinase assays with GST-CTD were performed with increasing amounts of recombinant GST or GST-MMTR, respectively. (C) Kinase assays with CAK on GST-CTD comparing inhibition activities of MMTR N-terminal and C-terminal half regions.