Figure 2.

Monovalent ions induce rapid folding of the pre-RNA. (A) RNA was annealed at 95°C in 50 mM Na-Hepes, pH 7.5/1 mM EDTA plus one of the following: no addition (−); 0.1, 0.25, 0.5, or 1 M NaCl; 0.1–1 M (NH₄)₂SO₄; or 6 mM MgCl₂, before electrophoresis on a native 6% polyacrylamide gel. The gel and running buffer contained 10 mM MgCl₂. (B) Pre-RNA was annealed as above with no salt (−), 1 M NaCl, 6 mM CaCl₂, or 6 mM MgCl₂. Samples were incubated for 30 s at 30°C with (+) or without (−) 0.1 mM GTP and 6 mM MgCl₂ immediately before loading. The MgCl₂ in the gel and running buffer was replaced by 10 mM CaCl₂.