In vitro activation of PKR (C121V, C135V). (A) Shown is a storage phosphor autoradiogram of a 10% SDS–polyacrylamide gel used to resolve PKR (C121V, C135V) autophosphorylated in response to various added concentrations of poly(I)·poly(C). Lanes 1–6, 0.012, 0.12, 1.2, 12, 120 and 0 µg/ml, respectively. (B) Plot of relative extents of PKR (C121V, C135V) autophosphorylation in the presence of different poly(I)·poly(C) concentrations.