The small free living soil nematode Caenorhabditis elegans, has been the subject of genetical and other studies in this laboratory for several years. Mutants have been isolated in many genes affecting its morphology and behaviour and a considerable amount is now known about its cellular anatomy and development. A subset of mutants with defective movement have severe alterations in the structure of body wall muscle cells. There are 95 muscle cells disposed in four quadrants which run the length of the animal beneath the cuticle. The musculature is obliquely striated and the sarcomeres are oriented parallel to the long axis of the animal. Disruption of the band structure can easily be detected in the living animal by polarized light microscopy and the defects can be more carefully analysed by electron microscopy. Two of the ten genes with altered muscle phenotypes have been shown to specify major structural proteins of muscle;
unc-54 codes for a major heavy chain of mysoin, while
unc-15 codes for paramyosin, the core protein of the thick filaments. As work with these genes developed, it became evident that it might be possible to use them as models for studying gene-protein relationships in a multicellular higher organism. This notion has been reinforced by the isolation of a large number of suppressors in the organism, some of which suppress specific alleles of the myosin and para-myosin genes. Although the molecular mechanism of these suppressors are unknown, it will be seen that their detailed study can now