Structure and control of assembly of cytoplasmic microtubules in normal and transformed cells

Indirect immunofluorescence analyses using antibodies directed against 6S tubulin have shown an elaborate cytoplasmic microtubule complex (CMTC) in nontransformed cells in culture. The CMTC is strikingly altered in cells that have been transformed spontaneously by viruses or by chemicals. Assembly of microtubules in vitro and in vivo is markedly inhibited in the presence of elevated levels of calcium. Alteration of the surface of normal cells by brief treatment with low concentrations of trypsin initiate a rapid breakdown of cytoplasmic microtubules. Finally, a hypothesis is presented relating microtubule assembly and surface membrane modulation suggesting that calcium is the primary modulating signal.