Myristoylated and nonmyristoylated forms of a protein are phosphorylated by protein kinase C.

Activation of protein kinase C is thought to require association of the kinase with the cell membrane. It has been assumed that cellular substrates for the kinase must likewise be associated with membranes, and previous studies with membrane-associated myristoylated proteins have supported this view. It is now shown that a mutation that prevents the normal amino-terminal myristoylation of a prominent cellular substrate of protein kinase C, and appears to prevent its membrane association, does not prevent the normal phosphorylation of this protein in intact cells in response to phorbol esters. Thus, membrane association may not be required in order for protein kinase C substrates to undergo phosphorylation.