REARRANGEMENT OF THE BACTERIAL CHROMOSOME USING Tn10 AS A REGION OF HOMOLOGY

The transposable tetracycline resistance element, TnlO, can serve as a region of homology to promote rec-dependent deletion, duplication and directed transposition of bacterial genes. TnlO insertions in regions of the chromosome near the histidine operon (his) have been isolated and characterized in Salmonella typhimurium. When strains are constructed containing two TnlO insertions flanking the his operon in the same orientation (TniO-his-TnZO), recombination can occur between TnZO sequences resulting in the deletion of the intervening his region. The sites of the TnZO insertions determine the endpoints of the deletion. In crosses designed toconstruct strains carrying Tn10-his-TnZO, another class of unstable recombinants arises in which the his region exists in tandem duplication, with a TnlO insertion joining the duplicated copies (his-TnlO-his). The sites of the parental TnZO insertions mark the endpoints of the duplication. When a strain carrying TnIO-his-TnZO is used as a donor of his+ in conjugation or P22-mediated transduction, recombinants can arise in which the his region has been transposed to the site of any Tn1O insertion, far from the normal location of his in the recipient chromosome. In this manner, the his operon has been moved to the site of a pyrB::TdO insertion and has been placed on F' plasmids. At these new locations, the his+ character shows the rec-dependent deletion of his+ expected for a TnZO-his-TnlO duplication. These methods should be generally useful for the manipulatioo of bacterial genes.