The Escherichia coli PrmA enzyme catalyzes methylation of the large ribosomal subunit protein L11. Database homology searches, multiple sequence alignment, and structure prediction allowed to dissect the primary structure of PrmA into two domains and assign putative functional or structural roles to invariant or highly conserved residues. Evolutionary relationships within the PrmA family were also analyzed. The topology of the branching order agrees to a large extent with the consensus phylogeny of Eubacteria, with the exception of beta and epsilon subdivisions of Proteobacteria, which most probably had their original prmA genes replaced by copies acquired via the lateral gene transfer from gamma-Proteobacteria and some close relative of the ancestor of gramnegative bacteria, respectively.