Junction sequences generated by 'one-ended transposition'.

In the presence of the cognate transposase, plasmids containing a single inverted repeat (IR) sequence of Tn21 or of Tn1721 can fuse efficiently with other plasmids ('one-ended transposition'). The junctions across the sequences of donor and recipient DNA in recombinants generated by this process have been determined. These show that the segment of donor DNA starts precisely at the IR sequence (it is variable at the other end), and is flanked by a direct repeat of host DNA (usually 5bp) that was present only once in the original host sequence. These are characteristics of recombinants generated by transposition of Tn21 and Tn1721 themselves, suggesting that the mechanism of one-ended transposition is very similar to that of the corresponding entire elements.