Identification of actin kinase activity in purified fragmin—actin complex

Actin kinase phosphorylates actin of fragmin—actin complex, resulting in the inactivation of the nucleation and capping activities of the complex. Fragmin—actin complex was prepared by a new purification procedure. Incubation with ATP caused inactivation of the purified complex and phosphorylation of actin of fragmin—actin complex. The detailed analysis of the complex by SDS-gel electrophoresis showed that actin kinase was co-purified with the fragmin—actin complex. Formation of such an association between actin kinase and substrate suggests that the kinase is localized on the fragmin—actin complex to efficiently regulate actin cytoskeletons.