MAP2 competes with MAP1 for binding to microtubules.

A question whether MAP1 and MAP2 (the major microtubule associated proteins from mammalian brain) bind to common or distinct sites on the microtubule surface was studied. Microtubules were assembled from tubulin and MAP1 and then centrifuged through a layer of MAP2 solution under conditions where no repolymerization of tubulin with MAP2 could occur. During centrifugation, MAP2 displaced most of MAP1 on the microtubules.

High molecular weight protein MAP 2 promoting microtubule assembly in vitro is associated with microtubules in cells.

Brain high molecular weight (HMW) protein promoting microtubule assembly in vitro and identical to MAP 2 (one of the proteins which copurify with tubulin through microtubule assembly-disassembly cycles), is shown to be associated with microtubules in interphase and mitotic cells. This HMW protein was purified earlier (Kuznetsov et al., 1978), directly from bovine brain without previous obtaining total microtubule protein.