Variation in the integration sites for Stx phages and LEE islands in O157 and non-O157 EHEC strains. (a) Locations of the Stx phages and the LEE islands on each chromosome are shown. Integration sites of Stx2 phages in O157 strain 3, O26 strain 8, and O111 strain 3, and those of Stx1 phages in O111 strains 1, 4, 5, and 6, and O103 strain 3 are unknown. (b-e) Schematic presentation of newly identified integration sites for Stx phages. DNA sequences of left or right junctions for each integration site are also shown. (b) The torS-tort intergenic region in O103 strains 1, 2, 4, and 6. The torS and torT genes encode a sensor for a two-component regulatory system and a periplasmic protein of unknown function, respectively. The right junction was not identified. (c) The argW region in O157 strain 8 and O103 strain 5. The argW gene encodes an arginine tRNA. (d) The ssrA region in O111 strains 2 and 3. The ssrA gene encodes the tmRNA. The right junction was not identified. (e) The prfC gene in O103 strain 5. The prfC gene encodes the peptide chain release factor (RF-3). Integration of Stx1 phage into the prfC gene changes the amino acid sequence of a short amino-terminal region of RF-3, and removes the authentic ribosome binding site and promoter sequences. It is not known whether the prfC gene is transcribed and/or translated in the strain. The prfC gene, however, is not listed as an essential gene of E. coli .