THE CAENORHABDITIS-ELEGANS-UNC-93 GENE ENCODES A PUTATIVE TRANSMEMBRANE PROTEIN THAT REGULATES MUSCLE-CONTRACTION

unc-93 is one of a set of five interacting genes involved in the regul ation or coordination of muscle contraction in Caenorhabditis elegans. Rare altered-function alleles of unc-93 result in sluggish movement a nd a characteristic "rubber band" uncoordinated phenotype. By contrast , null alleles cause no visibly abnormal phenotype, presumably as a co nsequence of the functional redundancy of unc-93. To understand better the role of unc-93 in regulating muscle contraction, we have cloned a nd molecularly characterized this gene. We isolated transposon-inserti on alleles and used them to identify the region of DNA encoding the un c-93 protein. Two unc-93 proteins differing at their NH2 termini are p otentially encoded by transcripts that differ at their 5' ends. The pu tative unc-93 proteins are 700 and 705 amino acids in length and have two distinct regions: the NH2 terminal portion of 240 or 245 amino aci ds is extremely hydrophilic, whereas the rest of the protein has multi ple potential membrane-spanning domains. The unc-93 transcripts are lo w in abundance and the unc-93 gene displays weak codon usage bias, sug gesting that the unc-93 protein is relatively rare. The unc-93 protein has no sequence similarity to proteins listed in current data-bases. Thus, unc-93 is likely to encode a novel membrane-associated muscle pr otein. We discuss possible roles for the unc-93 protein either as a co mponent of an ion transport system involved in excitation-contraction coupling in muscle or in coordinating muscle contraction between muscl e cells by affecting the functioning of gap junctions.