Figure 4.

UV melting profiles for wild-type VA RNA_I and compensatory base pair mutants. (A) Melting profiles collected at 280 nm for wild-type (black) and compensatory base pair mutant VA RNA_Is: AU1 (red), AU2 (orange), AU3 (light green), AU4 (dark green), AU5 (cyan), and AU6 (blue). (B) Melting profiles collected at 260 nm coloured as in (A). Note that the hypochromicity is significantly greater at 280 nm than 260 nm; however, compensatory base pair changes from G–C to A–U may increase the relative hypochromicity at 260 nm for the apparent transitions affected. Mutations in the Terminal Stem and Central Domain affect only the first apparent transition (T_m ∼60°C) while mutations in the Apical Stem affect only the second (T_m ∼83°C).