An ileX tRNA gene is located close to the Shiga toxin II operon in enterohemorrhagic Escherichia coli O157 and non-O157 strains

Abstract

A cosmid library of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL 933 was constructed and clones carrying the stx 2 gene were identified by colony blot hybridization with a stx 2 B specific probe. Nucleotide sequencing upstream of the stx 2 A gene revealed high sequence identities of 89.5% to the ileX tRNA gene found in E. coli. The ileX gene was located 260 bp from the translational start codon of stx 2 A. PCR analysis with primers specific for this analyzed region showed that in 11 Stx2-producing EHEC strains from patients with hemolytic uremic syndrome, all PCR-positive strains carried the ileX tRNA gene. However, PCR analysis of the respective region in 11 Stx1-producing EHEC strains detected no ileX genes. Although the role of ileX in Stx2-producing EHEC strains is not clear, its function in regard to the use of rare codons and as an integration site is discussed.