Myosins exist as homodimers of heavy chains: demonstration with specific antibody purified by nematode mutant myosin affinity chromatography.

The body-walls of Caenorhabditis elegans contain two different myosin heavy chains (Epstein, Waterston and Brenner, 1974) that associate to form at least two species of myosin (Schachat, Harris and Epstein, 1977a). To better define the distribution of these heavy chains in myosin molecules, we have characterized the myosin of C. elegans by immunochemical methods. Specific, precipitating anti-myosin antibody has been prepared in rabbits using highly purified nematode myosin as the immunogen. The difference in reactivity of the anti-myosin antibody with wild-type myosin containing both kinds of heavy chains (designated unc-54 and non-unc-54 heavy chains on the basis of genetic specification) and myosin from the mutant E190 that lacks unc-54 heavy chains Indicates that there are antigenic differences between myosin molecules containing unc-54 heavy chains and myosin molecules containing only non-unc-54 heavy chains. Antibody specific for the unc-54 myosin determinants has been prepared by the immunoadsorption of anti-myosin antibody with E190 myosin. This specific anti-unc-54 myosin antibody precipitates myosin that contains only unc-54 heavy chains. At the limits of resolution of our immunoprecipitation techniques, we could detect no heterodimeric myosin molecules containing both unc-54 and non-unc-54 heavy chains. The body-wall myosins of C. elegans therefore exist only as homodimers of either class of heavy chain.This specific anti-unc-54 myosin antibody promises to be a valuable tool in elucidating the role of two myosins in body-wall muscle and in molecular characterizations of mutant myosins in C. elegans. We report here the use of this antibody to detect antigenic differences between unc-54 myosin from the wild-type and the muscle mutant E675. In conjunction with the original anti-myosin antibody, other studies show that both unc-54 and non-unc-54 myosins exist within the same body-wall muscle cells (Mackenzie, Schachat and Epstein, 1978) and that both myosins are coordinately synthesized during muscle development in C. elegans (Garcea, Schachat and Epstein, 1978). We discuss the implications of the self-association of unc-54 and non-unc-54 myosin heavy chains into homodimeric myosins within the same body-wall muscles with respect to the assembly of thick filaments and their organization into a regular lattice.