Western Blot: RNA polymerase II [p Thr4] Antibody [TA336792] - Flag-tagged Rpb1 was IP'd with Flag antibody. Western blotting was performed using P-thr4 antibody. 26r: Rpb1 with 26 all-consensus YSPTSPS repeat CTD. T4V: Rpb1 with 30 YSPVSPS repeat CTD.