Figure 1. Phylogenetic relationships among major metazoan lineages and sequence of the DNA recognition loop in Rel Homology Domain proteins.

The phylogeny depicts the evolutionary relationships among taxa whose genomes have been sequenced. Multiple RHD proteins are encoded in the genomes of all of these animals except the nematode Caenorhabditis elegans, which appears to lack RHD proteins entirely, and the sponge, Amphimedon queenslandica, which appears to possess only a single RHD protein with similarity to NF-κB. The amino acid sequence of the DNA recognition loop is shown for every known RHD protein in these animals.