HETEROGENEITY OF THE AMINO-ACID-SEQUENCES OF ESCHERICHIA-COLI SHIGA-LIKE TOXIN TYPE-I OPERONS

PCR was used to amplify approx. 1470-bp segments of DNA containing com plete Shiga-like toxin type I(sltI) operons from Escherichia coli stra ins belonging to serotypes O48:H21, O111:H- and OX3:Hs. These fragment s were cloned and DNA sequence analysis identified several variations, as compared with published sltI sequences. All three sltI genes analy sed were more closely related to Shiga toxin-encoding genes (sht) of S higella dysenteriae type 1, than to previously published E. coli phage -encoded sltI genes. The greatest deviation in deduced amino acid (aa) sequence was observed in the SltI protein from the OX3:H8 strain, whi ch differed from the phage 933J-encoded SltI by 9 aa in the A subunit and 3 aa in the B subunit.