cdc2/pp56-62 are in vitro substrates for the tyrosine kinase encoded by the v-fms oncogene

In eukaryotic cells, the serine-threonine-specific kinase cdc2 induces entry into mitosis by phosphorylation of several proteins including cyclin (pp62) with which it forms a tight complex. We show here that cdc2 and several phosphoproteins in the range of 56 to 62 kilodaltons (kDa), associated with cdc2, serve as in vitro substrates for the v-fms-specific tyrosine kinase. This is the first demonstration of in vitro phosphorylation of a physiologically relevant substrate through the v-fms specific kinase. In addition, cdc2 phosphorylated the v-fms polypeptides in serine and threonine residues. The biological significance of the mutual phosphorylations is discussed.