sentence: copy numberDetermination of kanamycin resistance conferred by the constitutively expressed aph gene in RK2 and pUB307 showed that removal of the region with i10 increased resistance about 2-fold ( S1 Fig ) consistent with increased copy number.To determine whether the increased ability to cure is specific for F-like plasmids we inserted the IncK replication control region of archetypal plasmid R387 [ 30,31 ] as an anti-K cassette into both RK2 and pUB307 at the same location and tested for curing of R387 .