Dephosphorylation of pRB by anti-hemagglutinin immunoprecipitates from induced LLW02 cells. Samples were run in duplicate. Normal mouse IgG immunoprecipitate was used as a negative control. Anti-hemagglutinin immunoprecipitate, reaction run in the presence of okadaic acid (100 nM), a demonstrated PP1 inhibitor, was an additional negative control. Anti-hemagglutinin immunoprecipitate, revealing a decrease in 32P-labeled pRB band intensity, indicating removal of phosphate groups by 6His-HA-PP1α.