Binding of human SRP9/14 to mutated SRP RNAs. (A) Titration experiments with synthetic WT; 2L2 and 3L2 biotinylated RNAs. The binding reactions contained 40 nM h9/14 and tracer amounts of 35S-labelled h14 in complex with recombinant h9. WT RNA concentrations in lanes 1–8: 10, 20, 30, 40, 50, 100, 150 and 200 nM. 2L2 and 3L2 RNA concentrations in lanes 1–4: 60, 120, 240 and 480 nM. In, 50% of total protein used in the experiment. The bound protein was displayed by SDS–PAGE followed by autoradiography. (B) Quantitative analysis of the titration experiments. WT (diamonds), 2L1.2 (triangles), 2L2 (squares) and 3L2 (dots) RNAs. (C) Protein binding with the mutated synthetic SRP RNAs. The protein and RNA concentrations were 40 and 160 nM, respectively, in the binding reactions. The binding reactions of c54 also contained 40 nM recombinant h19. The quantification of the results is shown in Table 2.