Phylogenetic tree of the arg(A) homologues. The sequences have been collected, multiply aligned and used to reconstruct an evolutionary tree as described in Methods. The tree has been rooted using the acetyltransferase domain of NAGS sequences as an outgroup (subtree indicated with yellow color). The two other subtrees corresponding to the Arg(A) and ArgX sequences are indicated with pink and blue colors, respectively. Species names are according to SwissProt conventions (the detailed list is shown in Table 1).