Competitive DNase I footprinting assays between HlyU and H-NS on the upstream region of the rtxA1 operon promoter. (A) Increasing concentrations of HlyU and the fixed concentration of H-NS. Lane 1 and 2, no protein; lane 3, HlyU only (0.2 μM); lane 4, H-NS only (1.0 μM); lane 5-8, HlyU (0.2, 0.8, 1.5, 3.0 μM repectively) with the fixed concentration of H-NS (1.0 μM). (B) Increasing concentrations of H-NS and the fixed concentration of HlyU. Lane 1 and 2, no protein; lane 3, H-NS only (1.0 μM); lane 4, HlyU only (0.2 μM); lane 5-8, H-NS (0.2, 0.8, 1.5 and 3.0 μM repectively) with the fixed concentration of HlyU (0.2 μM). Lanes A, C, G and T represent the nucleotide sequencing ladders of pTopo-FP-P20481. Regions protected by H-NS are shown by the black bar, and region protected by HlyU is shown by the open bar.