Microtubule associated protein 1B (MAP1B) promotes efficient tubulin polymerisation in vitro.

The effect of MAP1B on tubulin polymerisation has been examined in reconstitution experiments using purified tubulin and MAP1B. Under the assembly conditions used, tubulin alone was incapable of polymerising, but addition of MAP1B resulted in rapid assembly into microtubules. The kinetics of MAP1B-promoted microtubule assembly examined using pseudo-first-order plots show that assembly is described by a single reaction rate. The calculated association rate constant for MAP1B was about 200 x 1096) M-1.s-1 and this constant was one order of magnitude higher when compared with that for MAP2-promoted assembly.