Analysis of Rev/RRE binding. RNA binding assays were conducted with [32P]-labelled RRE riboprobes and increasing concentrations of His-tagged Rev proteins, as described in Materials and Methods. Binding reactions containing increasing concentrations of His-tagged Matrix protein from HIV-1NL4-3 were included as negative controls. Rev/RRE complexes were resolved by electrophoresis in 5% (wt/vol) native polyacrylamide gels and visualized by autoradiography (A). Bands were quantified by phosphorimager analysis, and the percentage of RNA binding was calculated by dividing the signal intensity of bands associated with Rev/RRE complexes by the signal intensity of all bands, and multiplying this number by 100 (B). The data shown are representative of three independent experiments. *p < 0.01, Student's t test.