AN ILEX TRANSFER-RNA GENE IS LOCATED CLOSE TO THE SHIGA TOXIN-II OPERON IN ENTEROHEMORRHAGIC ESCHERICHIA-COLI O157 AND NON-O157 STRAINS

A cosmid library of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL 933 was constructed and clones carrying the stx(2) gene wer e identified by colony blot hybridization with a stx(2)B specific prob e. Nucleotide sequencing upstream of the stx(2)A gene revealed high se quence 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 st x(2)A. PCR analysis with primers specific for this analyzed region sho wed that in 11 Stx2-producing EHEC strains from patients with hemolyti c 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 us e of rare codons and as an integration site is discussed.