Abstract
Some transposable elements move by a replicative mechanism involving cointegrate formation. Intramolecular cointegration can generate a product called an "adjacent deletion" in which a contiguous chromosomal segment adjacent to the transposon is deleted while the element responsible remains intact. Insertion sequence IS10 is thought to transpose by a nonreplicative mechanism. In the simplest models, nonreplicative transposition cannot give rise to an adjacent deletion because an intrinsic feature of such transposition is excision of the IS element from the donor location. We report here that IS10 can generate adjacent deletions, but at a frequency which is approximately 1/30th the frequency of transposition for the same element. We suggest that these deletions might arise either by nonreplicative transposition events that involve two IS10 elements located on sister chromosomes or by aberrant nonreplicative events involving cleavage and ligation at only one end of the element.