unc-93 is one of a set of five interacting genes involved in the regulation or coordination of muscle contraction in Caenorhabditis elegans. Rare altered-function alleles of
unc-93 result in sluggish movement and a characteristic "rubber band" uncoordinated phenotype. By contrast, null alleles cause no visibly abnormal phenotype, presumably as a consequence of the functional redundancy of
unc-93. To understand better the role of
unc-93 in regulating muscle contraction, we have cloned and molecularly characterized this gene. We isolated transposon-insertion alleles and used them to identify the region of DNA encoding the
unc-93 protein. Two
unc-93 proteins differing at their NH2 termini are potentially encoded by transcripts that differ at their 5' ends. The putative
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 acids is extremely hydrophilic, whereas the rest of the protein has multiple potential membrane-spanning domains. The
unc-93 transcripts are low in abundance and the
unc-93 gene displays weak codon usage bias, suggesting 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 protein. We discuss possible roles for the
unc-93 protein either as a component of an ion transport system involved in excitation-contraction coupling in muscle or in coordinating muscle contraction between muscle cells by affecting the functioning of gap junctions.