The Xenopus XMAP215 and its human homologue TOG proteins interact with cyclin B1 to target p34cdc2 to microtubules during mitosis

Cytoskeleton reorganization, leading to mitotic spindle formation, is an M- phase-specific event and is controlled by maturation promoting factor (MPF: p34cdc2-cyclinB1 complex), It has previously been demonstrated that the p3 4cdc2-cyclin B complex associates with mitotic spindle microtubules and tha t microtubule-associated proteins (MAPs), in particular MAP4, might be resp onsible for this interaction. In this study, we report that another ubiquit ous MAP, TOG in human and its homologue in Xenopus XMAP215, associates also with p34cdc2 kinase and directs it to the microtubule cytoskeleton, Costai ning of Xenopus cells with anti-TOGp and anti-cyclin B1 antibodies demonstr ated colocalization in interphase cells and also with microtubules througho ut the cell cycle. Cyclin B1, TOG/XMAP215, and p34cdc2 proteins were recove red in microtubule pellets isolated from Xenopus egg extracts and were elut ed with the same ionic strength. Cosedimentation of cyclin B1 with in vitro polymerized microtubules was detected only in the presence of purified TOG protein. Using a recombinant C-terminal TOG fragment containing a Pro-rich region, we showed that this domain is sufficient to mediate cosedimentatio n of cyclin B1 with microtubules, Finally, we demonstrated interaction betw een TOG/XMAP215 and cyclin B1 by co-immunoprecipitation assays. As XMAP215 was shown to be the only identified assembly promoting MAP which increases the rapid turnover of microtubules, the TOG/XMAP215-cyclin B1 interaction m ay be important for regulation of microtubule dynamics at mitosis. (C) 2000 Academic Press.