Assembly of nonneural microtubules in the absence of glycerol and microtubule-associated proteins.

Microtubule protein from Ehrlich ascites tumor cells purified by an in vitro polymerization process in the absence of glycerol and calcium chelators contains several accessory proteins but lacks the high molecular weight proteins which are present in neurotubulin. DEAE-Sephadex chromatography of two-times cycled tubulin removes these nontubulin proteins, resulting in pure tubulin, as critically examined by sodium dodecyl sulfate gel electrophoresis. This tubulin can readily assemble into microtubules in assembly buffer, at low magnesium concentrations, without glycerol and at tubulin concentrations above 0.8 mg/mL. Electron microscopy shows that the tubules are identical with normal microtubules. When the purified tubulin fraction was reduced and carboxymethylated, a significant minor protein component could be observed electrophoretically, migrating between alpha- and beta-tubulin. At present, the identity and function of this protein are not known. The results demonstrate that the in vitro assembly of tubulin from Ehrlich ascites tumor cells does not require high molecular weight proteins or gamma-like factor(s) as has been proposed for the neurotubulin system.