Differential phosphorylation of microtubule proteins by ATP and GTP.

Purified brain microtubule protein is phosphorylated by endogenous protein kinase activities in the presence of [gamma-32P] ATP or [gamma-32P] GTP. Here we show that certain microtubule-associated proteins are phosphorylated differently by GTP or ATP as direct phosphoryl donors, suggesting the presence of distinct kinase activities, with different specificities, associated with microtubule protein.