Plasmid copy number. Autoradiogram of a Southern blot of total DNA digested with HindIII and probed simultaneously with The Ω-Spc cassette, located within recA gene (chromosomal detector) and with a pDOP vector (incoming plasmid detector). The plasmid copy number of each strain was calculated as the ratio of the integrated hybridization signal of repC (incoming plasmid) and the integrated hybridization signal of Ω-Spc cassette (chromosome). Lane 1, CFNX107; lane 2, CFNX107/pDOP-C; lane 3, CFNX107/pDOP-αC; lane 4, pDOP-H3. Numbers at the bottom indicate the plasmid/chromosome ratio.