Three genomic fragments homologous to cut-1 of Caenorhabditis elegans (C. elegans) have been identified in the intestinal parasitic nematode Ascaris lumbricoides (A. lumbricoides). Two of these fragments identify one region of the A. lumbricoides genome; they are separated by 8-9 kb and have opposite orientation, with the direction of transcription converging toward the center of the region. The third gene, which has been studied more completely, is in a different region of the genome separated from the first one by not less than 12-15 kb. The complete genomic sequence of this third gene has been determined. cDNA overlapping clones were obtained from adult A. lumbricoides RNA via the rapid amplification of cDNA ends (RACE) procedure [Frohman et al., 1988. Rapid production of full-length cDNAs from rare transcripts: amplification using a single gene-specific oligonucleotide primer. Proc. Natl. Acad. Sci. USA 85, 8998-9002] and sequenced. The mature mRNA of this gene, which we have named ascut-1, is trans-spliced to the spliced leader sequence of nematodes (SL1) [Krause, M., Hirsh, D., 1987. A trans-spliced leader sequence on actin mRNA in C. elegans. Cell 49, 753-761]. The mRNA is 1684 nt long plus the poly(A) tail and contains four exons with a 138 nt untranslated 5' leader and a 388 nt untranslated 3' tail. Conceptual translation of the coding sequence shows a protein of 385 aa with a signal peptide of 16 aa. The protein shows very high homology with CECUT-1, the product of the C. elegans gene cut-1 and with other cuticlin proteins of nematodes. A 262 amino acids region which is strongly conserved between these proteins seems to identify a group of proteins, so far restricted to nematodes, for which the name CUT-1-like is proposed.