In vitro and in vivo characterization of pp39mos association with tubulin.

The product of protooncogene c-mos, pp39mos, is expressed and functions during oocyte maturation. We have previously found that pp39mos is complexed with and phosphorylates tubulin. In addition, part of pp39mos is localized on mitotic spindle and spindle pole regions in c-mosxe-transformed NIH/3T3 cells. Here, we further characterized the interaction between pp39mos and tubulin. We show that mos product synthesized in vitro appears in a 500 kD complex and can oligomerize with tubulin in vitro under tubulin polymerization conditions. Moreover, conditions which favor microtubule depolymerization facilitate pp39mos extraction from c-mosxe-transformed NIH/3T3 cells. We also show by immunofluorescence and immunoelectron microscopy that pp39mos is localized on microtubules. Thus, in vitro and in vivo the mos product is associated with tubulin and microtubules, respectively. Therefore, the mos product may be involved in the modification of microtubules and formation of the spindle.