Figure 2.—

Phylogenetic tree of OIR and OIR′ domains. A possible position for the root, based on the species phylogeny, is marked. The domains (94- to 123-residues long) were aligned using MUSCLE (Edgar 2004). The tree was constructed by maximum likelihood using PHYML (Guindon and Gascuel 2003) using the JTT substitution model and four rate classes. Branch lengths are drawn to scale, indicating the number of amino acid substitutions per site. Bootstrap support for the branch separating OIR and OIR′ domains was 94% (100 replicates).