ACTIVATION OF TYPE-1 PROTEIN PHOSPHATASE BY CDC2 KINASE

Purified cdc2 or cdc2 obtained from HeLa cells in association with p13suc1) activate inactive type-1 protein phosphatase (PP1) (catalytic subunit . inhibitor-2 complex, purified from skeletal muscle). Likewise in the case of PP1 activation by F(A)/GSK3, activation by cdc2 is accompanied by accompanied by phosphorylation of inhibitor-2 (I2) and free I2 can be phosphorylated as well. Correlation between PP1 activation and I2 phosphorylation is suggested by the fact that both activation and phosphorylation (a) increase in parallel during incubation with cdc2, (b) decrease in parallel upon subsequent cdc2 inhibition by EDTA, and (c) are inhibited by the cdc2 inhibitor 5,6-dichlorobenzimidazole riboside. cdc2 also phosphorylates the catalytic subunit of PP1, whether in the complex with I2 or as free molecule. The activation of PP1 by cdc2 and by F(A)/GSK3 is compared.