Effect of MAP 1, MAP 2, and tau-proteins on structural parameters of tubulin assemblies.

When temperature-dependent recycling procedures for purification were used, tubulin is usually accompanied by a mixture of microtubule-associated proteins (MAPs) primarily comprising MAP 1, MAP 2, and the tau-proteins. Formerly we reported that microtubules formed from tubulin in the presence of these MAPs have more protofilaments than those formed without MAPs. Furthermore, these MAPs suppress the formation of aberrant assemblies (Böhm et al., BBA 800, 119, 1984). Now, we report that each single MAP fraction is able to influence the protofilament number of microtubules and the ratio between aberrant assemblies and microtubules in the same manner as the MAP mixture. This implies that all the MAPs investigated play a certain role in lateral association of tubulin dimers.