XMAP215 regulates microtubule dynamics through two distinct domains

XMAP215 belongs to a family of proteins involved in the regulation of micro tubule dynamics, In this study we analyze the function of different parts o f XMAP215 in vivo and in Xenopus egg extracts. XMAP215 has been divided int o three fragments, FrN, FrM and FrC (for N-terminal, middle and C-terminal, respectively), FrN co-localizes with microtubules in egg extracts but not in cells, FrC colocalizes with microtubules and centrosomes both in egg ext racts and in cells, while FrM does not colocalize with either centrosomes o r microtubules, in Xenopus egg extracts, FrN stimulates microtubule growth at plus-ends by inhibiting catastrophes, while FrM has no effect, and FrC s uppresses microtubule growth by promoting catastrophes. Our results suggest that XMAP215 is targeted to centrosomes and microtubules mainly through it s C-terminal domain, while the evolutionarily conserved N-terminal domain c ontains its microtubule-stabilizing activity.