  We propose a stochastic model that accounts for the growth, catastrophe and
rescue processes of steady state microtubules assembled from MAP-free tubulin.
Both experimentally and theoretically we study the perturbation of microtubule
dynamic instability by S-methyl-D-DM1, a synthetic derivative of the
microtubule-targeted agent maytansine and a potential anticancer agent. We find
that to be an effective suppressor of microtubule dynamics a drug must
primarily suppress the loss of GDP tubulin from the microtubule tip.
