The E. coli gene encoding heat stable toxin is a bacterial transposon flanked by inverted repeats of IS1

Restriction endonuclease subclones of the Escherichia coli gene encoding the heat stable (ST) toxin exhibit a stem and loop structure similar to those seen in many procaryotic transposons. An EcoRI DNA fragment encoding tetra-cycline (Tc) resistance but no transposition functions was spliced into the ST gene in one of these subclones. By monitoring Tc^r, we were able to show that the ST gene transposes. Restriction and DNA sequence data strongly suggest that the ST transposon, Tn1681, is flanked by inverted repeats of IS1.