Duplication of an insertion sequence during transpositional recombination

The genomes of a wide variety of eukaryotic and prokaryotic organisms contain segments of DNA that can move from one location to another and can mediate other genetic rearrangements. Many different transposons have been identified in Gram-negative bacteria and extensively characterized. Most of them fall into one of two groups: the rather homogeneous Tn3 family of transposons, and the more heterogeneous collection of insertion sequences (IS). The result of an IS-mediated deletion is a new junction between one end of the IS and the target DNA; the other IS end remains at its original location. Using a selective procedure to obtain intramolecular events promoted by IS903 in a RecA- host, we have shown that the most frequent event is the formation of adjacent deletions. These deletions occur at normal frequencies only if both IS ends are intact, suggesting that the deletion-distal IS end also participates in the recombination.