Transposition of IS1-lambdaBIO-IS1 from a bacteriophage lambda derivative carrying the IS1-cat-IS1 transposon (Tn9)

Summary Tn9 is a transposable element in which a gene (cat) determining chloramphenicol resistance is flanked by directly repeated sequences that are homologous to the insertion sequence IS1. We show here that infection of Escherichia coli K12 (under Rec^- Red^- Int^- conditions) with a bio transducing phage carrying Tn9 results in the formation of bio transductants as frequently as cat transductants (about 1 per 10⁶ to 10⁷ infected cells). Most of the bio transductants do not carry cat, just as most of the cat transductants do not carry bio. In spite of the absence of cat, the bio prophage can transpose a second time, from the E. coli chromosome to different sites on an F gal plasmid. Analysis of the structure of the transposed bio element, by restriction nuclease digestion and by electron microscopy, demonstrates that the integrated bio prophage is flanked by directly repeated IS1 elements. We conclude that there is no genetic information for the ability to transpose encoded in the non-repeated portion of Tn9, i.e. that the directly repeated IS1 elements alone are responsible for Tn9 transposition.