Modulation of some parameters of assembly of microtubules in vitro by tyrosinolation of tubulin.

Using tyrosinolated and detyrosinolated tubulins, we have compared several parameters of microtubule assembly in vitro. Rates and extents of polymerization were the same under all conditions, but microtubules assembled from detyrosinolated tubulin in the presence of crude microtubule-associated proteins (MAPs) or subsaturating MAP-2 contained a smaller proportion of the MAPs. Preliminary results indicate that this may be a function of the phosphorylation state of MAP-2. Tyrosinolated tubulin assembled into relatively shorter microtubules in the presence of saturating MAP-2. When assembly was induced with substoichiometric concentrations of taxol, in place of MAPs, the rate and extent of assembly were about twice as great with tyrosinolated tubulin.