FIGURE 7.

RcnR is less formaldehyde-responsive but RcnR^S2P gains reactivity. A, β-galactosidase activity in SL1344 containing rcnR-P_rcnRA (solid bars) or rcnR^S2P-P_rcnRA (open bars) fused to lacZ grown to mid-exponential phase in M9 minimal medium in the absence or presence of MNIC formaldehyde (50 μm) or CoCl₂ (1 μm). Values are means of three biological replicates (each performed in triplicate) with S.D. (error bars). B and C, anisotropy change upon titration of a high concentration of rcnRAPro (2.5 μm) with RcnR in the presence of 5 mm EDTA (B) or a limiting concentration of rcnRAPro (10 nm) with RcnR in the presence of 5 mm EDTA (black symbols) and with the addition of 50 μm formaldehyde (open symbols) or Ni(II)-RcnR (light gray symbols) and Co(II)-RcnR (dark gray symbols) in the presence of 5 μm NiCl₂ or 5 μm CoCl₂, respectively (C). Symbol shapes represent individual experiments. Data were fit to a model describing a 2:1 protein tetramer (nondissociable)/DNA stoichiometry (binding with equal affinity) (50, 86), and lines represent simulated curves produced from the average (apparent) K_DNA determined across the experimental replicates shown. D, apparent K_DNA values of RcnR (black symbols) and RcnR^S2P (open symbols) with increasing formaldehyde concentration. Values are means of three replicates with S.D. E, as described in C except with RcnR^S2P in the presence of 5 mm EDTA (black symbols) and with the addition of 50 μm formaldehyde (open symbols).