The multiple phosphorylation of the microtubule-associated protein MAP2 controls the MAP2:tubulin interaction.

Pre-phosphorylation of the microtubule-associated protein MAP2 with the co-purifying cAMP-independent protein kinase (a) decrease the affinity of MAP2 for taxol-stabilised microtubules, (b) increases the dissociation rate constant for microtubule polymerisation, each of which is dependent upon the level of phosphorylation, but (c) has no effect on the association rate constant. Microtubule assembly has no effect on the kinetics of phosphorylation, whereas phosphorylation of pre-assembled microtubules causes their immediate depolymerisation at a rate which is proportional to the initial rate of phosphorylation. The results suggest that the modulated phosphorylation of MAP2 may regulate microtubule length in vivo.