Figure 3.

Binding curves for the interaction of wild-type S7 and its mutant derivatives with str mRNA. The curves show binding isotherms measured by a nitrocellulose filter binding assay. They correspond to the wild-type protein and to representative examples of mutations that affect binding modestly, strongly or dramatically. The portion of the str mRNA containing the S7 binding site was synthesized in vitro and incubated with increasing amounts of protein. Apparent association constants (K′_a) between the str mRNA and S7 or its mutant derivatives were calculated from the binding isotherms and are presented in Table 1.