Multiple sequence alignment and domain architectures of the MedPIWI family. (A) Multiple sequence alignment with representatives of the classical PIWI module is shown. Organization, numbering, labeling, consensus abbreviations, and coloring of the alignment are as described in the legend to Figure 2. Conserved residues involved in nucleotide binding across both the classical and MedPIWI modules are denoted above the appropriate column in the alignment by “*”. Residues which may be conserved in classical PIWI modules but not in the MedPIWI module are denoted by “%”. (B) Representative domain architectures of the MedPIWI module. The small green box immediately upstream of the MID domain represents the conserved, small “linker” domain. Other unlabeled domains represent potential lineage-specific domains while C×C refers to the animal-specific, potential zinc-binding domain (see Additional file 1). Organism abbreviations may be found in Additional file 1.