ELONGATION FACTOR-1-ALPHA STABILIZES MICROTUBULES IN A CALCIUM CALMODULIN-DEPENDENT MANNER/

Elongation factor-1 alpha. (EF-1 alpha), a highly conserved protein na med for its role in protein translation, is also a microtubule-associa ted protein (MAP). We used high-resolution differential interference c ontrast microscopy to quantify the effect of substoichiometric amounts of EF-1 alpha (isolated from Daucus carota) on the dynamic instabilit y of microtubules assembled in vitro from either animal or plant tubul in. EF-1 alpha modulates the dynamic behavior of microtubules assemble d from either tubulin source, resulting in longer and more persistent microtubules. EF-1(alpha), at a 1:20 molar ratio to tubulin, significa ntly (P < 0.05) reduces the frequency of catastrophe threefold and dec reases shortening velocities almost twofold for microtubules assembled from animal tubulin. For microtubules assembled from plant tubulin, s ubstoichiometric amounts of EF-1 alpha significantly (P < 0.05) suppre ss the frequency of catastrophe greater than twofold and causes an alm ost threefold reduction in shortening velocities. Elongation velocitie s increase almost twofold and rescues, which are not observed in the a bsence of EF-1 alpha, occur. In addition, calcium/calmodulin (Ca2+/CaM ), which regulates the ability of EF-1 alpha to bundle taxol-stabilize d microtubules in vitro, also modulates the effect of EF-1 alpha on th e dynamic behavior of microtubules assembled in vitro from animal tubu lin. Microtubule severing in the presence of EF-1 alpha was never obse rved. These data support the hypothesis that EF-1 alpha modulates the dynamic behavior of microtubules assembled in vitro in a Ca2+/CaM-depe ndent manner. Cell Motil. Cytoskeleton 41:168-180, 1998. (C) 1998 Wile y-Liss, Inc.