Competition of IntI1 binding to the bottom strand of the aadA1 attC site and supershift experiments with anti-IntI1 antibody. Lane 1, control DNA; lane 2, IntI1 control binding reaction; lanes 3 to 6, competition by the unlabeled attC bottom strand; addition of 2-, 10-, 20-, and 40-fold excess unlabeled bottom-strand aadA1 attC, respectively; lanes 7 and 8, competition by attC top strand; addition of an identical (lane 7) or twofold (lane 8) excess amount of the top attC aadA1 strand; lanes 9 and 10, heterologous DNA competition; addition of an identical (lane 9) or twofold (lane 10) excess amount of the unrelated competitor (an oligonucleotide mix); lanes 11 to 13, supershift assays with specific antisera; lane 11, incubation of IntI1 with polyclonal anti-IntI1 antibody before binding reaction; lane 12, incubation with polyclonal anti-IntI1 antibody after binding reaction; lane 13, incubation with preimmune serum after binding reaction. ds, dsDNA; ss, ssDNA; I and II, different protein-DNA complexes.