Elongation factor‐1α stabilizes microtubules in a calcium/calmodulin‐dependent manner

Abstract

Elongation factor-1α (EF-1α), a highly conserved protein named for its role in protein translation, is also a microtubule-associated protein (MAP). We used high-resolution differential interference contrast microscopy to quantify the effect of substoichiometric amounts of EF-1α (isolated from Daucus carota) on the dynamic instability of microtubules assembled in vitro from either animal or plant tubulin. EF-1α modulates the dynamic behavior of microtubules assembled from either tubulin source, resulting in longer and more persistent microtubules. EF-1α, at a 1:20 molar ratio to tubulin, significantly (P < 0.05) reduces the frequency of catastrophe threefold and decreases shortening velocities almost twofold for microtubules assembled from animal tubulin. For microtubules assembled from plant tubulin, substoichiometric amounts of EF-1α significantly (P < 0.05) suppress the frequency of catastrophe greater than twofold and causes an almost threefold reduction in shortening velocities. Elongation velocities increase almost twofold and rescues, which are not observed in the absence of EF-1α, occur. In addition, calcium/calmodulin (Ca2+/CaM), which regulates the ability of EF-1α to bundle taxol-stabilized microtubules in vitro, also modulates the effect of EF-1α on the dynamic behavior of microtubules assembled in vitro from animal tubulin. Microtubule severing in the presence of EF-1α was never observed. These data support the hypothesis that EF-1α modulates the dynamic behavior of microtubules assembled in vitro in a Ca2+/CaM-dependent manner. Cell Motil. Cytoskeleton 41:168–180, 1998. © 1998 Wiley-Liss, Inc.