A 60-KDA PLANT MICROTUBULE-ASSOCIATED PROTEIN PROMOTES THE GROWTH ANDSTABILIZATION OF NEUROTUBULES IN-VITRO

The search for microtubule-associated proteins (MAPs) in plants is rel atively recent. In particular, the ''classical MAPs,'' which stimulate the polymerization and stabilization of microtubules, have only been examined in heterogeneous fractions, As a first step in dissecting the role of individual MAPs, we have chromatographically purified a singl e 60-kDa protein from a carrot MAP fraction and analyzed its effects o n tubulin assembly. MAP60 promoted the formation of long, morphologica lly regular brain microtubules in vitro, an effect inhibited by preinc ubation of the MAP with affinity-purified antibodies against this prot ein, MAP60 also increased the stability of microtubules to dilution an d significantly enhanced cold stability to the normally cold-sensitive neurotubules. These in vitro properties are consistent with a role fo r MAP60 in regulating the turnover/assembly of dynamic plant microtubu les in vivo.