Direct activation of cdc2 with phosphatase: identification of p13suc1-sensitive and insensitive steps

In Xenopus oocytes, activation of MPF during prophase-metaphase transition is associated with the tyrosine dephosphorylation of the cdc2 protein. In vivo and in cell-free extracts kinase activation can be inhibited by excess p13suc1, a subunit of the protein kinase. Here we have demonstrated that affinity-purified cdc2 from Xenopus prophase oocytes may be activated in vitro by exposure to potato acid phosphatase. In vitro, excess p13 does not inhibit tyrosine dephosphorylation of prophase cdc2, but nonetheless binds and prevents the activation of the enzyme. By contrast, fully activated enzyme from metaphase Xenopus eggs is insensitive to excess p13. These observations define a p13-sensitive state in the activation of fully active cdc2 that follows tyrosine dephosphorylation