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

Abstract

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 MW proteins which are present in neurotubulin. DEAE-Sephadex chromatography of 2-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 Mg concentrations, without glycerol and at tubulin concentrations above 0.8 mg/mL. Under EM, 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. The identify and function of this protein are not known. The in vitro assembly of tubulin from Ehrlich ascites tumor cells apparently does not require high MW proteins or .tau.-like factor(s) as proposed for the neurotubulin system.