Evidence against tubulin oligomer dissociation to tubulin dimer at assembly temperatures.

Chromatography of microtubule protein through 8% agarose at 4 and 31 degrees C demonstrated that tubulin oligomer was not dissociated to tubulin dimer and microtubule associated proteins by assembly temperatures. During chromatography, formation of microtubules was prevented by using 10 microM podophyllotoxin and/or 25 microM GTP. In the presence of 25 microM GTP, tubulin oligomer at 31 degrees C and microtubule protein retained the ability to polymerize. Evidence against dimer formation from tubulin oligomer was also obtained via a turbidity study of the initial events (the first 90 s) of microtubule assembly.