Upper part. Schematic representation of the Cre-mediated recombination between Insertion vector pINS-Neo and Target vector phrGFP. Lower part. XL1 Blue (pir+) and BW23474 (pir-) E. coli strains were transformed by the pINS-Puro, phrGFP vectors (50 ng each) and the recombination mix (Neo × GFP). 1/10th of the transformed cells was selected on the LB plates containing either ampicillin or kanamycin. Insertion vector pINS-Neo containing R6Kγ can transform pir+ but not pir- strain and produces kanamycin-resistant colonies. Target vector phrGFP containing pUC-origin can transform pir+ as well as pir- strain and produces ampicillin-resistant colonies. Recombination mix contains initial vectors as well as the product of recombination and thus can transform both pir- and pir+ strains and produce ampicillin and kanamycin-resistant colonies. Only the recombination product containing both pUC-origin and Kan-marker can produce kanamycin-resistant colonies of the pir- strain.