FIG. 2.

Binding of MarR to marO assayed by a restriction enzyme site protection assay. In the absence of MarR, the SspI recognition sequence in marO is not protected and the plasmid is cut into two pieces of 3,472 bp (fragment B) and 1,104 bp (fragment C) in length. A single cut in the non-marO SspI restriction site results in fragment A (4,576 bp) and indicates protection of the SspI site in marO. Serial increases in the concentration of MarR led to increased protection, as indicated by the conversion of the two smaller bands, fragments B and C, to a single 4,756-bp fragment. MW, molecular weight standards; U, uncut pSup-Test from the original plasmid preparation; L, pSup-Test digested with BamHI (linear form); D, pSup-Test digested with SspI (double-cut form).