The Plant Cell , Vol. 6 , 893-905, June 1994, © 1994 American Society of Plant Physiologists

Neil A. Durso and Richard J. Cyr
The Pennsylvania State University, Department of Biology, University Park, PA


A Calmodulin-sensitive Interaction between Microtubules and a Higher Plant Homolog of Elongation Factor-1-alpha

    Figures' index

  1. (2K jpeg) SDS-PAGE analysis of carrot proteins isolated by tubulin affinity chromatography and of cosedimentation assays for MT binding proteins present in the affinity-isolated proteins.
  2. (2K jpeg) SDS-PAGE analysis of the selective purification of pp50 using CaM affinity chromatography and of the retention of pp50's MT binding activity assessed by cosedimentation.
  3. (7K jpeg) Dark-field microscopy of the MT bundles induced by the presence of pp50-containing protein and the Ca2+/CaM-dependent dissociation of these bundles.
  4. (text table) Alignments of amino acid sequences of tryptic peptide fragments of pp50 with corresponding sequences of EF1a homologs.
  5. (4K jpeg) Evidence for direct binding between pp50 and MTs.
  6. (3K jpeg) Analysis by SDS-PAGE followed by immunoblotting of pp50's cosedimentation with taxol-stabilized MTs of pure carrot tubulin, and of pp50's electrophoretic comigration with carrot alpha-tubulin.

© 1994 American Society of Plant Physiologists
(from Durso & Cyr 1994, Plant Cell, 6: 893-905)

Abstract

The microtubules (MTs) of higher plant cells are organized into arrays with essential functions in plant cell growth and differentiation; however, molecular mechanisms underlying the organization and regulation of these arrays remain largely unknown. We have approached this problem using tubulin affinity chromatography to isolate carrot proteins that interact with MTs. From these proteins, a 50 kD polypeptide was selectively purified by exploiting its Ca2+-dependent binding to calmodulin (CaM). This polypeptide was identified as a homolog of elongation factor-1a (EF-1a) a highly conserved and ubiquitous protein translation factor. The carrot EF-1a homolog bundles MTs in vitro, and moreover, this bundling is modulated by the addition of Ca2+ and CaM together -- Ca2+/CaM. A direct binding between the EF-1a homolog and MTs was demonstrated, providing novel evidence for such an interaction. Based on these findings, and others discussed herein, we propose that an EF-1a homolog mediates the lateral association of MTs in plant cells by a Ca2+/CaM-sensitive mechanism.

Keywords: Calcium; Calmodulin; Carrot cells; Elongation factor-1-alpha; Microtubule-associated protein.


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