Co-IP of RNAPII with anti-cyclin C (αcyclinC), anti-cdk8 (αcdk8), and anti-HA (αHA) from nuclear extracts of cells without or with expressed, HA-tagged rv-cyclin. Co-precipitates were detected successively on western blots with antibodies specific for phosphorylated forms of the RNAPII CTD: H5 (phospho-Ser2; YSPTSPS), H14 (phospho-Ser5; YSPTSPS), and 8WG16 (un-phosphorylated RNAPII). The position of a 191 KDa marker is indicated to illustrate the size difference between un-phosphorylated RNAPII (predicted molecular weight 220 KDa) and the hyperphosphorylated forms (apparent molecular weight of 240 to 250 KDa).