Table 1 Description of the phylogenetic groups 1–5 and the number of E. coli enzymes in each group. For instance, an E. coli enzyme which has at least one representative in one or more eukaryotes but not in archaea is a group 2 enzyme. The fourth column contains the number of enzymes which are proposed examples of horizontal gene transfer. The phylogenetic classification is based on the phylogenetic tree in Figure 2.

From: Preferential attachment in the evolution of metabolic networks