Simple assay for quantitation of Tn5 inversion events in Escherichia coli and use of the assay in determination of plasmid copy number.

In this report, we describe a simple method for measuring the frequency of sequence inversion in the transposable element Tn5 as a result of recombination across its duplicated IS50 elements. The structure of Tn5 was manipulated so that the neomycin phosphotransferase gene of the transposon would be expressed only if a sequence inversion event occurred. This highly sensitive assay also served as the basis for a novel means of estimating plasmid copy number.