Replicon fusion mediated by a single-ended derivative of transposon Tn1721

Tn1722 delta 1K, a derivative of transposon Tn1721 lacking one terminal inverted repeat (IR) and conferring kanamycin resistance, promotes transposition of the resistance marker to a target replicon at about 100-fold lower frequency than the wild-type element. A study involving restriction analysis of 16 independent Tn1722 delta 1K-mediated events led to the following results: (i) Tn1722 delta 1K mediates fusions of the donor (pRU506) and target (RSF1010) replicons; the fused entities are non-permuted. (ii) Tn1722 delta 1K promotes insertions of donor DNA at many different sites in the target replicon. (iii) The analyzed fusion plasmids contain the entire target and various lengths of donor DNA. Eleven products contain the entire donor plasmid plus a duplication of the IR (class A), whereas five products contain only portions adjacent to the single IR (class B). (iv) In each case the two replicons are joined at (or very close to) the single IR. The second junction is located shortly beyond the duplicated IR in class A and at different sites within the donor plasmid in class B. These results are interpreted in terms of asymmetric replicative transposition.