Analysis of structure and microtubule assembly activity of the Drosophila 205K MAP.

Phosphorylation, dimerization and binding to calmodulin have been reported to influence the microtubule assembly capacities of MAPs (microtubule-associated proteins). Here we report that the Drosophila 205K MAP is a phosphoprotein in vivo and can be phosphorylated by cdc2/p34 in vitro. Bacterially produced 205K MAP is competent of microtubule assembly and microtubule bundling and binds to immobilized calmodulin in a Ca2+-dependent way. EM rotary shadowing analyses suggest that 205K MAP consists of an amino-terminal flexible extended region and a carboxy-terminal globular domain. This carboxy-terminal region harbors the microtubule binding site and sequences required for dimerization, as confirmed by in vitro crosslinking experiments of truncated proteins.