Worm Breeder's Gazette 11(1): 34
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Using the Ascaris des homeobox AHB-1 as a probe we isolated two genomic clones from C. elegans, y CELHO, see WBG 10(2),1988, p. 36) and ceh- 12. Ceh-11 maps in the region of egl-5. Ceh-12 maps to the first chromosome, to the right of dpy-6 (A. Coulson and J. Sulston, personal communication). Out of more than 100 published sequences, the homeodomain with the highest level of similarity with ceh-11 was X1Hbox2, an Antp class homeodomain from X. laevis. The sequence of the second homeobox clone (ceh-12) is interrupted by an intron located upstream of the codon for the amino acid 45, inside the putative recognition helix. Most interestingly an intron at the same position, was found in five other known homeoboxes, namely two in C. elegans e in D. melanogaster ( labial, Distalless and proboscipedia). The conservation of intron position between evolutionary quite distant species could reflect some unknown function or selective constraint. On the same genomic clone, we found a tRNA(Arg) gene (rtr-1) by sequence analysis. This tRNA decodes CGU, the most used Arg codon in C. elegans.In a further approach we used the ceh-11 homeobox to screen the Ahringer egg cDNA library. In one of the positive clones we found a third homeobox (ceh- 13). The most similar homeodomains to ceh-13 were hox-1.6 (a murine homeobox) with 43 residues identical out of 60 and lab with 41 residues identical out of 60. Therefore ceh-13 seems to belong to the labial subclass of homeoboxes. Furthermore, the similarity between ceh-13 and lab extends somewhat downstream of the homeobox, the amino acids 61, 62, 65 and 66 being identical. Recently we have isolated the corresponding genomic clone and are currently investigating the structure of the ceh-13 gene. Our three homeodomains have an Arg at position 9 of their recognition helix. According to the theory proposed by S. Hanes and R. Brent in their recent Cell paper (Cell 57, 1989, p. 1275-1283) we speculate that our C. elegans homeodomains have an Antp type DNA- binding specificity. [See Figure 1]