Duplication of insertion element IS50 associated with Tn5 transposition inAzospirillum brasilense

The characterization of a DNA fragment with a Tn5 insertion in a regulatory nif gene of Azospirillum brasilense is reported. Restriction endonuclease mapping, Southern hybridization with a Tn5 probe, and nucleotide sequencing revealed that IS50 had duplicated in Tn5. The duplication of an IS50 eleme nt suggests the occurrence of a replicative mechanism of transposition. A s trategy, based on the bacterial ability of homologous recombination that wa s used to precisely eliminate Tn5 along with the duplicated IS50 element, i s presented.