New positive selection system based on the parD (kis/kid) system of the R1plasmid

The use of vectors that are designed to allow positive selection of recombi nants facilitates cloning experiments in E. coli. Using kid, a lethal gene of the RI plasmid parD locus, we generated pKID vectors leading to high sel ective efficiency of recombinants (greater than 90%). The E. coli bacterial host used to propagate these vectors produces the Kis protein, the natural antagonist of Kid. This new positive-selection system exhibits the same ef ficiency as the original ccdB-based selection vectors, pKIL (4). We also sh ow that the ccdB and kid systems are independent. This property increases t he potential of plasmidic poison-antidote systems for genetic applications and opens the door to a generation of new vectors containing the two select ion systems.