The global regulator crp has undergone predominantly vertical evolution. Crp has conserved context, and the gene tree is concordant with the species tree except for the Pasteurellacea and perhaps Sodalis. The incongruent placement of Sodalis is not supported by a nucleotide sequence tree (data not shown). The deep branching of the Pasteurellacea is strongly supported, and two swaps would be required to make its placement concordant with the species tree. An insertion of crp into Pasteurellacea is unlikely because of the conserved proximity of the functionally unrelated gene yheT. Instead, the placement probably reflects homologous recombination or long branch attraction. In any case, this does not affect the lineage leading to Escherichia coli, and so we classified crp as native. The crp tree shown was computed from protein sequences with phyml and 100 bootstraps (as in Figure 3).