The Use of Transposons to Introduce Well-Defined Deletions in Plasmids: Possibilities for in Vivo Cloning

A method for obtaining well-defined deletions in an octopine Ti plasmid was developed. It was based on the assumption that deletions would occur between two directly repeated transposons, when both are temporarily present in one plasmid molecule. To obtain such a situation, recombination has been forced between Agrobacterium tumefaciens Ti plasmids, each carrying the transposon Tn1831 at a different position. In a number of cases, most probably when the transposons are directly repeated, deletion formation indeed occurred and at high frequency. Mutants were isolated carrying Ti plasmids with one copy of Tn1831, and the region of DNA, between the positions of the transposons in the original plasmid, deleted. Moreover, in the case that the segment of DNA, enclosed by the two transposons, harbors the requirements for autonomous replication of an R plasmid, it is shown that in vivo cloning of such a segment of the Ti plasmid on the R plasmid can be accomplished.