The complete tropomyosin gene, designated tmy-1, of Caenorhabditis elegans was recovered by genome walking from a fragment that was obtained by exon-expression cloning using specific cloning using specific anti-tropomyosin antiserum as a probe. The genome structure of the tmy-1 gene has been determined by combining the DNA sequences of cDNA clones with those of the genomic fragments. The single-copy gene spans approximately 13 kb and include 14 exons. Comparison of cDNA and genomic sequences demonstrates that three isoforms are encoded by the gene tmy-1. Homology of the 27 C-terminal amino acid residues to those of Drosophila and vertebrates suggest that these may be the body wall, pharyngeal and non-muscle types. Tissue-specific expression of the tmy-1 gene was determined by microinjection of a promoter/lacZ fusion gene and with immunohistochemistry by using affinity-purified tissue-specific anti-tropomyosins. The 5' end promoter common to CeTMI and CeTMII is expressed in the body wall muscles, vulva, anus muscles and male tail muscles. Control sequences of the 5' end promoter are located 660 to 800 bp upstream of the initial methionine codon. The third isoform, CeTMIII, encoding 256 amino acids residues was expressed in the pharyngeal muscles by the promoter in the third intron. The mRNA of CeTMIII was trans-spliced with SL1 and SL2. These results allow is to solve the question of what is common from this worm to vertebrates, and also what are the cross-species complexities and the tissue-specific differences of tropomyosins. The tmy-1 gene is located on the C. elegans genomic YAC grid near the right end of chromosome I, in the region on the lev-11 gene.