Plasmids containing insertion elements are potential transposons.

Abstract

In vivo recombination between the plasmid pHS1, a temperature-sensitive replication mutant carrying tetracycline resistance, and pSM1, a small plasmid carrying 1 copy of the insertion element IS1 was studied [in Escherichia coli]. Recombinant plasmids were found by selection for tetracycline resistance at 42.degree. C. Their formation was independent of recA function. Analysis of the physical structures of various recombinant DNA molecules with EM and restriction endonucleases revealed that pSM1 was integrated at its IS1 into numerous sites on pHS1, giving rise to a duplication of IS1 in the same orientation at both junctions. Nucleotide sequence analysis of recombinant plasmids and their parental plasmid DNA revealed that 9 nucleotides at a target site were duplicated at the junction of each IS1. This phenomenon implies that plasmids containing a translocatable DNA element can be potential transposons.