Physical Analysis of Tn10- and IS10-Promoted Transpositions and Rearrangements

Michael M. Shen ¹, Elisabeth A. Raleigh ¹, and Nancy Kleckner ¹

¹ Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138

We have investigated by Southern blot hybridization the rate of IS10 transposition and other Tn10/IS10-promoted rearrangements in Escherichia coli and Salmonella strains bearing single chromosomal insertions of Tn10 or a related Tn 10 derivative. We present evidence for three primary conclusions. First, the rate of IS10 transposition is approximately 10^-4 per cell per bacterial generation when overnight cultures are grown and plated on minimal media and is at least ten times more frequent than any other Tn 10/IS10-promoted DNA alteration. Second, all of the chromosomal rearrangements observed can be accounted for by two previously characterized Tn10-promoted rearrangements: deletion/inversions and deletions. Together these rearrangements occur at about 10% the rate of IS10 transposition. Third, the data suggest that intramolecular Tn10-promoted rearrangements preferentially use nearby target sites, while the target sites for IS 10 transposition events are scattered randomly around the chromosome.

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