Figure 7.

Missing contact probing with ArgR binding to the lrp control region. (A) Depurination (citrate) and (B) depyrimidination (hydrazine). Sparingly modified DNA molecules incubated in the absence (I = input) and in the presence of various concentrations of ArgR, resulting in approximately 50% binding for F1 and B1, and > 90% for F2 and B2, were separated on basis of their affinity for the protein by gel electrophoresis in native conditions, extracted from gel, cleaved at the positions of modification with piperidine and equal amounts of the reaction products separated by gel electrophoresis in denaturing conditions. Positions that upon base removal interfere strongly or moderately are indicated. Positions that upon removal result in better binding are indicated with orange colored letters (C) Nucleotide sequence of the ArgR binding site in the lrp control region with indication of positions that upon modification interfere strongly (filled symbols) or moderately (open symbols) with ArgR binding are indicated. Orange colored symbols represent inverse effects. ARG box sequences separated by a 3 bp spacer are numbered 1 to 18 for the top (coding) strand and 1′ to 18′ for the bottom strand in the 5′-3′ direction.