Stabilization of microtubules by GTP analogues.

We recently demonstrated that the nonhydrolyzable analogues of GTP (GMPPCP and GMPPNP) and ATP support the elongation phase of tubulin assembly and are incorporated into the E-site of polymerized tubulin. In this report we studied the stability of microtubules containing GTP analogues by examining length redistributions after shearing at polymer steady state. The mean length of a population of microtubules containing GMPPCP increased only by 37% over a 150 min time period after shearing. Microtubules which contained 70% ATP and 30% GDP at the E-site increased in length by 88%. In contrast, the mean length of microtubules assembled in the presence of GTP increased by 410% in the same time period. These results suggest that microtubules containing GMPPCP or ATP at their ends are stabilized from depolymerization.