Control of microtubule dynamics by the antagonistic activities of XMAP215 and XKCM1 in Xenopus egg extracts

Microtubules are dynamic polymers that move stochastically between periods of growth and shrinkage, a property known as dynamic instability, Here, to investigate the mechanisms regulating microtubule dynamics in Xenopus egg e xtracts, we have cloned the complementary DNA encoding the microtubule-asso ciated protein XMAP215 and investigated the function of the XMAP215 protein . Immunodepletion of XMAP215 indicated that it is a major microtubule-stabi lizing factor in Xenopus egg extracts. During interphase, XMAP215 stabilize s microtubules primarily by opposing the activity of the destabilizing fact or XKCM1, a member of the kinesin superfamily. These results indicate that microtubule dynamics in Xenopus egg extracts are regulated by a balance bet ween a stabilizing factor, XMAP215, and a destabilizing factor, XKCM1.