Gel mobility shift assays with purified AerR. The first lane of each gel had only 32P-labeled probe and heparin (1,000-fold excess), while the second lane had the same probe and heparin preincubated with 2 μM AerR. puc, crtAI, puf, and bchC represent the various promoter probes that were used with each probe containing two CrtJ recognition sequences. P- represents the mobility of the unshifted probe, while -S represents the mobility of the AerR-shifted probe.