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.