Reactions were performed in 20 mM Tris-HCl/80 mM KCl, pH 7.2, at 37°C. (A) c-Jun LZ36 (60 µM) + RNA18 (170 µM); reaction time, 4 h; column, 3.14 mL Nucleosil C-18 300-5 (Macherey & Nagel). (B) Recombinant c-Jun (20 µM) + RNA18 (90 µM); reaction time, 48 h; column, 2.5 mL Eclipse XDB C-18 (Agilent). (C) c-Jun + RNA18 (as in B) in the presence of 1 U of the ribonuclease A inhibitor RNasin. (D) RNA18; incubation time, 48 h. Resolution of the digestion products by the two different HPLC columns required a different gradient set-up (30-mL gradient in panel A versus 13-mL gradient in panels B, C and D). The elution profiles are presented relative to the percentage of acetonitrile in the two gradients (dashed blue lines). Asterisk (*) marks the position of intact RNA18.