Hydrolysis of GTP associated with the formation of tubulin oligomers is involved in microtubule nucleation

Hydrolysis of GTP is known to accompany microtubule assembly, Here we show that hydrolysis of GTP is also associated with the formation of linear oligomers of tubulin, which are precusors (prenuclei) in microtubule assembly. The hydrolysis of GTP on these linear oligomers inhibits the lateral association of GTP-tubulin that leads to the formation of a bidimensional lattice, Therefore GTP hydrolysis interferes with the nucleation of microtubules. Linear oligomers are also formed in mixtures of GTP-tubulin and GDP-tubulin. The hydrolysis of GTP associated with heterologous interactions between GTP-tubulin and GDP-tubulin in the cooligomer takes place at a threefold faster rate than upon homologous interactions between GTP-tubulins. The implication of these results in a model of vectorial GTP hydrolysis in microtubule assembly is discussed.