FIGURE 3.

(a) The fraction of specific sequence complex formed after one hour incubation decreases as the concentration of noncognate oligonucleotide increases. EcoRI (1.5 nM) was incubated with specific sequence DNA fragment (3 nM) and varying concentrations of noncognate oligonucleotides in 75 mM NaCl, 20 mM imidazole (pH 7.0), 3.6 Osm betaine, and at 20°C. The gel mobility shift assay was used to monitor specific complex formation. (b) The dependence of the specific EcoRI-DNA complex fraction on TAATTC sequence oligonucleotide concentration for the gel shown in panel a. (c) The linear dependence of on confirms the concentration dependence predicted by Eq. 4. The dissociation rate constant, k₄, of the TAATTC “star” sequence oligonucleotide complex can be calculated from the slope. For this particular experiment, k₄ is 0.86 min⁻¹.