FIG 1 .

Phylogenetic tree indicating the node and taxa of the ancestral and modern tuf (EF-Tu) homologs. Pink circles represent the ancestral EF-Tu nodes. E. coli was genetically engineered to carry ancestral or modern homologs of tuf, encoding translation elongation factor EF-Tu, replacing the native E. coli tufA gene. A shaded box indicates the area of viability of EF-Tu gene exchange. The scale bar expresses units of amino acid substitutions per site. The tree was created with data from references 35 and 38.