Effects of microtubule-associated proteins on network formation by neurofilament-induced polymerization of tubulin.

It has been revealed that neurofilaments stimulate polymerization of tubulin and thereby cause gelation. Addition of a very small amount of MAPs to the reaction mixture of tubulin and neurofilaments resulted in promotion of gelation. This could not be ascribed to MAP-induced cross-linking between microtubules and neurofilaments because further increases in the MAP concentration (still substoichiometric amount) resulted in total suppression of gelation. It is concluded that MAPs promote microtubule assembly independently of neurofilaments, and lower the concentration of tubulin available for neurofilament-induced polymerization, then preventing network formation.