Figure 1.

(A) Immunoblot of electrophoretically separated lysates of HeLa cells reacted with antibody to HA tag. HeLa cells were mock transfected or transfected with cytomegalovirus expression plasmids carrying HA-tagged dominant-negative cdc2 (pCMVcdc2-dn). The cells were harvested 36 h after transfection, solubilized, electrophoretically separated on 10% bisacrylamide gels, and probed with antibody to HA. (B) Autoradiographic image of histone H1 phosphorylated in vitro by immunoprecipitated cdc2. HeLa cells were infected with HSV-1(F) 36 h after transfection with pCMVcdc2-dn and incubated for an additional 14 h at 37°C. Histone H1 was mixed with immune-precipitated Cdc2 from harvested, lysed cells. The reaction mixtures were separated on denaturing gels as described in Materials and Methods.