Excision of transposon Tn5 is dependent on the inverted repeats but not on the transposase function of Tn5.

The excision of Tn5 from sites of insertion in the Escherichia coli genome was studied by examining the reversion of lac::Tn5 insertion mutations to lac+. We find that: (i) the frequency of excision depends on the site of Tn5 insertion, (ii) excision occurs efficiently in recA- cells, (iii) excision does not require a Tn5-encoded transposition function, and (iv) efficient excision requires the inverted repeats of Tn5. We propose that excision of Tn5 is similar to the formation of spontaneous deletions and occurs by slippage during DNA synthesis.