In this paper we examine the role of two myosins in body-wall muscle cells of the nematode Caenorhabditis elegans. Large populations of nematodes are synchronized, and the synthesis and accumulation of myosin heavy chains and total protein are followed through postmitotic larval development. Growth is exponential with time for both the wild-type N2 and the body-wall muscle-defective mutant E675, with a longer doubling time for the mutant. Utilizing the electrophoretic polymorphism of the E675 myosin heavy chains, we show that distinguishable classes of heavy chains accumulate differentially throughout development. Immunochemical measurements confirm a similar result in N2. Total myosin heavy chain accumulation is also quantitatively similar for the two chains. Myosin heavy chain relative synthetic rates as determined by pulse-labeling are constant throughout development and are equivalent for the two strains. The final fraction of accumulated
unc-54 to total heavy chains of approximately 0.63 equals the constant synthetic fraction of approximately 0.62. Since myosin heavy chain accumulation and relative synthesis are equivalent, we conclude that the turnover of heavy chains is also similar in N2 and E675 despite the extensive structural and functional disruption within body-wall muscle cells of the latter strain. Since the accumulated fraction of
unc-54 myosin heavy chains reaches a plateau at the constant synthetic fraction, myosin accumulation in the body-wall muscle cells may be attributed to a constant ratio of synthetic rates of the two body-wall myosin species. The coordinate synthesis of two myosins in the same body-wall muscle cells is