In vitro inhibition of tubulin assembly by a ribonucleoprotein complex associated with the free ribosome fraction isolated from Xenopus laevis oocytes: effect at the level of microtubule-associated proteins.

The 100 000 X g supernatant prepared from defolliculated Xenopus laevis oocytes inhibits, in a dose-dependent manner, the in vitro polymerization of rat brain neurotubulin. The oocyte inhibitory factor is thermolabile, totally inactivated by RNAse and partially by trypsin. A preliminary purification of the inhibitor showed that it is associated with the free oocyte ribosomes (80 S). The saturable binding of microtubule-associated proteins, essentially MAP2, to this 80 S ribonucleoprotein fraction is responsible for the inhibition of the in vitro tubulin assembly.