unc-45 gene of Caenorhabditis elegans encodes a muscle-specific tetratricopeptide repeat-containing protein

The unc-45 gene of the nematode, Caenorhabditis elegans, is essential for muscle organization and embryonic development. Genetic evidence suggests the unc-45 gene product controls muscle thick filament assembly. We report here on the determination of the gene's chromosomal location and the isolation and sequencing of its cDNA. The amino terminus of the predicted unc-45 protein contains three tandem repeats that belong in the tetratricopeptide repeat family. Tetratricopeptide motifs have been shown to be involved in protein interactions, and some of the closest homologues have chaperone-like activity. The carboxy terminus of the protein has homology with the related fungal proteins, CRO1 and She4p, which have been postulated to play a role in assembly of or interactions with a cytoplasmic myosin. We have also determined the sequence of the homologous gene from C. briggsae, which demonstrates a high level of conservation. We show that the unc-45 gene promoter can drive reporter gene expression, which is limited to muscle tissues (pharyngeal, body wall, vulval, and anal muscles), consistent with a role for the unc-45 gene in muscle development or function.