FIGURE 6.
Interaction of SvtR with oligonucleotides 36m, 39m, 70m, 120m, and nonspecific DNA (poly[dIG,dC]) followed by fluorescence. A, binding of SvtR to fluorescein-labeled 36m oligonucleotide (flDNA). Fluorescence intensity (arbitrary units) as a function of total protein concentration. The solid line corresponds to the fit of the data (Equation 1 in the supplemental material) The dissociation constant (KD,fl) of the SvtR pair of dimers-flDNA complex obtained by non-linear least squares fitting was 1.6 ± 0.2 nm. B, competition of unlabeled DNA with fluorescein-labeled flDNA. Unlabeled oligonucleotides were added to 5 nm flDNA-100 nm protein samples. Poly[dIG,dC] was used as a nonspecific competitor in an independent assay. Solid lines correspond to fits of the data to Equation 5 in the supplemental material. The IC50,u values in nm units were, in decreasing affinity order 0.3 ± 0.2 (120m, ▵), 0.7 ± 0.2 (70m, ●), 1.3 ± 0.1 (39m, □), 1.6 ± 0.3 (36m, ○), and 15.2 ± 1.7 (poly[dIG,dC], ▾).