PubMed1994
p34cdc2 protein is found in prophase, metaphase and activated Xenopus oocytes at a similar level whereas its kinase activity oscillates within meiosis. Using an anti-PSTAIRE antibody that recognizes Xenopus p34cdc2, it was demonstrated that the major part of p34cdc2 was associated with microtubules isolated in vitro from Xenopus oocytes. Conversely, tubulin was recovered in association with p34cdc2 in p13-Sepharose pellets. The abundance of the fraction of p34cdc2 which was associated with microtubules did not oscillate during the meiotic maturation and the activation process. By contrast, the histone H1 kinase activity of p34cdc2 estimated in microtubular oocyte pellets was much higher in metaphase than in prophase oocytes. Cyclin B, which is associated in vivo with p34cdc2 in prophase and metaphase oocytes, was also present in the microtubular fractions. However, cyclin was not necessary for the binding of p34cdc2 to microtubules since p34cdc2 from activated eggs, where cyclin was missing, still copurified with microtubules. Purified MAP2, but not tubulin, was able to bind to p34cdc2, demonstrating that the association between p34cdc2 and microtubules was mediated by microtubule-associated proteins. During the meiotic maturation of Xenopus oocytes, several protein kinases were activated, among them MAP kinase. MAP kinase also associated with microtubules. It was demonstrated that both p34cdc2 kinase and MAP kinase purified from Xenopus oocytes were able to phosphorylate in vitro rat brain MAP2. However both protein kinases phosphorylated different domains of MAP2, suggesting that they might regulate microtubules in different ways.