History of L27 domain shuffling. (a)Phylogeny of the MPPsubfamily, based on the GuKdomain maximum likelihood tree. (b)The L27-1domain phylogeny showing the inferred domain insertion event. (c)Reconstruction of the evolution of the MPPdomain architecture, showing the replacement of the N-terminal L27domain in the common ancestor of MPP2and MPP6. Clades containing mouse, human, and chicken orthologs are collapsed.