The wild-type conformation of the Mos-1 inverted terminal repeats is suboptimal for transposition in bacteria.

The two inverted terminal repeats (ITRs) flanking the Mos-1 mariner element differ in sequence at four positions. Gel retardation experiments indicated that each of these differences has a significant impact on the quality of the interaction between the ITR and the Mos-1 transposase. We showed that the transposase binds to the 3' ITR better than to the 5' ITR. The results of transposition assays performed in Escherichia coli indicated that these differences have an influence on the rate of transposition and the stability of the transposition products. Finally, we find that the wild-type configuration of the Mos-1 element, with one 5' ITR and one 3' ITR, is less efficient for transposition in bacteria than that of an element having two 3' ITRs.