Figure 1.

Position-Specific Ser Phosphorylation of RNAPII CTD by CDKD and CDKD-Activating CDKF;1 Kinases.

(A) CDKF;1 phosphorylation of CDKDs is abolished by Ala exchange of conserved T-loop Thr residues indicated in parentheses. kD, molecular mass standard.

(B) CDKF;1 and CDKDs are self-activated by autophosphorylation and phosphorylate the GST-CTD substrate. Kinase-substrate combinations used in the assays are indicated.

(C) Immunoblotting of CDKF;1 and CDKD GST-CTD kinase assays with antibodies recognizing specifically the CTD S₂P, S₅P, and S₇P positions. See also Supplemental Figure 4 online.