DYNAMIN is a microtubule-binding protein with a microtubule-activated GTPase activity1,3. The gene encoding dynamin is mut-ated in shibire4,5, a Drosophila mutant defective in endocytosis in nerve terminals and other cells6-9. These observations place dyna-min into two distinct functional contexts, suggesting roles in microtubule-based motility or in endocytosis. We report here that dynamin is identical to the neuronal phosphoprotein dephosphin (P96), originally identified by its stimulus-dependent dephosphorylation in nerve terminals10-13. Dynamin is a protein doublet of Mr 94 and 96K arising by alternative splicing of its primary transcript. In the nerve terminal, both forms of dynamin are phosphorylated by protein kinase C (PKC) and are quantitatively dephosphoryla-ted on excitation. In vitro, dynamin is also phosphorylated by casein kinase II which inhibits PKC phosphorylation. Phosphory-lation by PKC but not by casein kinase II enhances the GTPase activity of dynamin 12-fold. The dynamins are therefore a group of nerve terminal phosphoproteins whose GTPase is regulated by phosphorylation in parallel with synaptic vesicle recycling. The regulation of dynamin GTPase could serve as the trigger for the rapid endocytosis of synaptic vesicles after exocytosis.
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