A CALMODULIN-SENSITIVE INTERACTION BETWEEN MICROTUBULES AND A HIGHER-PLANT HOMOLOG OF ELONGATION FACTOR-1-ALPHA

The microtubules (MTs) of higher plant cells are organized into arrays with essential functions in plant cell growth and differentiation; ho wever, molecular mechanisms underlying the organization and regulation of these arrays remain largely unknown. We have approached this probl em using tubulin affinity chromatography to isolate carrot proteins th at interact with MTs. From these proteins, a 50-kD polypeptide was sel ectively purified by exploiting its Ca2+-dependent binding to calmodul in (CaM). This polypeptide was identified as a homolog of elongation f actor-1 alpha a (EF-1 alpha)-a highly conserved and ubiquitous protein translation factor. The carrot EF-1 alpha homolog bundles MTs in vitr o, and moreover, this bundling is modulated by the addition of Ca2+ an d CaM together (Ca2+/CaM). A direct binding between the EF-1 alpha hom olog and MTs was demonstrated, providing novel evidence for such an in teraction. Based on these findings, and others discussed herein, we pr opose that an EF-1 alpha homolog mediates the lateral association of M Ts in plant cells by a Ca2+/CaM-sensitive mechanism.