C. elegans body wall muscle thick filaments are assembled from two different types of myosin heavy chain, MHC A and MHC B. The structural gene for the MHC A protein has been identified from the reaction of bacterial fusion peptides with specific monoclonal antibodies. We have also shown that a mutation in the sup-3
locus that enhances the accumulation of the MHC A protein is closely linked to the MHC A gene. A model of sup-3
action is proposed.