A microtubule-associated protein specific to differentiated neuroblastoma cells.

A modified procedure is reported that enables microtubule assembly to occur in extracts of differentiated neuroblastoma cells. Of the proteins that co-assemble through five successive cycles, only two, with molecular weights of 215,000 and 71,000, are retained in constant ratio to tubulin. The 215,000-dalton protein is quantitatively sedimented with microtubules during later cycles of assembly, whereas the 71,000-dalton protein is distributed between assembling and nonassembling fractions. Similar procedures do not induce assembly for microtubules from nondifferentiated neuroblastoma cells. Two-dimensional gel analyses indicate that the differentiated cell extracts contain the 215,000-dalton protein. In contrast, gels of extracts from nondifferentiated cells show no protein in the equivalent region. These data suggest that the 215,000-dalton protein is a microtubule-associated protein that may play a role in microtubule-dependent neurite differentiation.