3 NEW CLASSES OF MUTATIONS IN THE CAENORHABDITIS-ELEGANS MUSCLE GENE SUP-9

We are studying five interacting genes involved in the regulation or c oordination of muscle contraction in Caenorhabditis elegans. A distinc tive ''rubber-band'' muscle-defective phenotype was previously shown t o result from rare altered-function mutations in either of two of thes e genes, unc-93 and sup-10. Null mutations in sup-9, sup-10, sup-18 or unc-93 act as essentially recessive suppressors of these rubber-band mutations. In this work, we identify three new classes of sup-9 allele s: altered-function rubber-band, partial loss-of-function and dominant -suppressor. The existence of rubber-band mutations in sup-9, sup-10 a nd unc-93 and the suppression of these mutations by null mutations in any of these three genes suggest that these proteins are required at t he same step in muscle contraction. Moreover, allele-specific interact ions shown by the partial loss-of-function mutations indicate that the products of these interacting genes may physically contact each other in a multiple subunit protein complex. Finally, the phenotypes of dou ble rubber-band mutant combinations suggest that the rubber-band mutat ions affect a neurogenic rather than a myogenic input in excitation-co ntraction coupling in muscle.