Characterization of F-actin bundling activity of Tetrahymena elongation factor 1 alpha investigated with rabbit skeletal muscle actin.

Elongation factor 1 alpha (EF-1 alpha) is an essential factor for protein synthesis in eukaryotes. Here, we demonstrated that Tetrahymena EF-1 alpha induced bundles of rabbit skeletal muscle F-actin as well as Tetrahymena F-actin in vitro, although Tetrahymena and skeletal muscle actins are different in some parts of their primary structures and in the binding abilities to some actin-binding proteins. Co-sedimentation experiments showed that the binding ratio of Tetrahymena EF-1 alpha to skeletal muscle F-actin in the bundles was 1 : 1. Electron microscopic observation showed that alkaline pH or high ionic strength reduced the bundling activity of Tetrahymena EF-1 alpha to some extent, although the EF-1 alpha seemed to be able to induce bundling of the F-actin within the range of physiological condition.