Escherichia coli heat-labile enterotoxin genes are flanked by repeated deoxyribonucleic acid sequences

Publisher Website
Google Scholar
Abstract
The enterotoxin regions of the heat-labile and heat-stable enterotoxin (LT+ ST+) plasmid, pJY11, originating in a clinically isolated E. coli strain, were isolated as various-sized DNA fragments by using cloning vehicles. The structure of the LT+ region and its neighboring DNA regions was studied by using these recombinant plasmids. The LT+ region consisted of at least 2 genes, toxA and toxB, which could complement each other in trans. The toxA- and toxB-encoded polypeptides (LT subunits A and B, respectively) were identified by their immunological cross-reactivity with Vibrio cholerae enterotoxin subunit A or B. These tox genes and the promoter(s) were localized with respect to the restriction endonuclease cleavage map. The LT+ region was flanked by repeated DNA sequences (designated as .beta.). Another tox gene(s), encoding ST (designated as toxS), which was also flanked by inverted, repeated DNA sequences (designated as .alpha.), was located between 1 of the .beta. sequences and the LT+ region. These novel DNA structures (.beta.-.alpha.-toxS-.alpha.-toxA-toxB-.beta.) suggest the possibility that the LT+ region is on a transposon containing an ST transposon within the structure.