Nomenclature & Abbreviations A listed gene name means that gene carries a loss of function mutation, a Δ preceding a gene name means the gene is deleted. If a gene is not listed, it is not known to be mutated. Prophages present in wt K-12 strains (F, λ, e14, rac) are listed only if absent. E. coli B strains are naturally lon– and dcm–. F– = Does not carry the F plasmid F+ = Carries the F plasmid.