MICROTUBULE-ASSOCIATED PROTEIN 1B (MAP1B) PROMOTES EFFICIENT TUBULIN POLYMERIZATION IN-VITRO

The effect of MAP1B on tubulin polymerisation has been examined in rec onstitution experiments using purified tubulin and MAP1B. Under the as sembly conditions used, tubulin alone was incapable of polymerising, b ut 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 reactio n rate, The calculated association rate constant for MAP1B was about 2 00 x 10(6) M(-1). s(-1) and this constant was one order of magnitude h igher when compared with that for MAP2-promoted assembly.