The regulatory role of the IS 1‐encoded InsA protein in transposition

Summary We show here that the protein InsA, which is encoded by IS 1 and binds specifically to the terminal inverted repeats of this insertion sequence, negatively regulates IS 1 transposition activity. We demonstrate that it inhibits both IS 1‐mediated cointegrate formation and transposition of a synthetic IS 1‐based transposon (‘omegon’Ω‐on). These results also indicate that the Ω‐on which does not itself encode IS 1 transposition functions can be complemented in trans , presumably by the copies of IS 1 resident in the Escherichia coli chromosome. Using insA‐lacZ gene fusions, we show that at least part of this effect can be explained by the ability of InsA to repress expression of IS 1‐encoded genes both in cis or in trans. The experiments involving Ω‐on transposition raise the possibility that InsA inhibits transposition directly by competition with the transposase for their cognate site within the ends of IS 1.