Fig. 2. ceh-23 and ttx-3 sequences and alleles. (A) Relationship of the CEH-23 homeodomain to its most closely related homeodomains. Although the CEH-23 homeodomain bears a strong affinity to the distal-less and empty spiracles protein families, other C. elegans proteins represent the true Dll and ems orthologs. CEH-23 appears to have no ortholog in other species, suggesting that CEH-23 may have arisen by a gene duplication event in the nematode lineage. C. elegans proteins are bold and underlined. Homeodomains that show the highest similarity to the CEH-23 homeodomain were identified by BLAST searches (including searches of the 11/23/00 release of the C. elegans genome, the 11/6/2000 release of the human genome sequence and the 9/16/2000 release of the Drosophila genome sequence) and assembled into a phylogenetic tree using the pileup/distances/growtree algorithms of the GCG package with default parameters. The tree is rooted with LIM and POU homeodomain proteins (not shown). (B) ceh-23(ms23) deletion allele. (C) ttx-3 mutant alleles. The upper panel shows the schematic localization of the nucleotide changes in ttx-3 alleles. The lower panel shows the corresponding amino acid changes in the homeodomain. mg158 contains a missense mutation in one of the most highly conserved residues of the homeodomain, F49 (homeodomain numbering), which appears to be indispensable for the structural integrity of homeodomains (Gehring et al., 1994). nj14 was provided by Ikue Mori; due to its molecular similarity to ot22, it was not further characterized.
