A set of non-complementing, closely-linked, ethyl methanesulphonate-induced mutations in Caenorhabditis elegans specifically affects the structure and function of body-wall muscle cells but not the pharyngeal musculature. One of these mutations,
e675, is semidominant and results in the production of a new protein of about 203,000 molecular weight in addition to normal myosin at about 210,000 Mr. The abnormal polypeptide chain is structurally very similar to normal myosin heavy chain when maps of iodinated peptides are compared. The E675 mutant shows a clear relation between defective movement, disruption of the body-wall muscle structure, and the molecular defect in the myosin heavy chains. The altered chain is snythesized in heterozygotes, suggesting that the
e675 mutation is either in a structural gene for the heavy chain or in a cis acting control element. The hypothesis that there are two classes of myosin heavy chain within the same cells is discussed.