FIG. 4.

Gel mobility shift assays of PKR-flAlu RNA complexes. Labeled flAlu RNA was incubated with the indicated amounts of PKR[K296R] and assayed by gel electrophoresis. The positions of free probe, high- (C1) and low (C2)-mobility complexes, and wells are indicated. Phosphorimager analysis was used to measure the amounts of free RNA and complexes; the dissociation constant of complex C1 was 0.26 μM. As discussed in the text, the dissociation constant for C2 was model dependent. Assuming that C2 results from occupancy of two PKR binding sites within flAlu RNA, the estimated dissociation constant for the PKR complexes associated with each site was 0.24 μM.