Phylogenetic relationships of the PRC-barrel-containing proteins along with the domain architectures. The phyletic pattern of each family is shown, along with the number of proteins (if there is more than one). Species abbreviations are as in Figure 3. The RELL bootstrap values for the major branches are shown at their base. The thickness of a given branch is approximately proportional to the number of proteins contained within it. Ysnf, a repeat domain typified by the Bacillus subtilis YsnF protein; N-term, the specific amino-terminal domain of the RimM proteins.