Figure 3:

The difference between R_FRET for the base paired (H-JBP-H) control and H-J-H in (a) KCl and (b) MgCl₂, where J represents either J5/5a or JU₄U₅. Dashed red lines mark a salt concentration above which one of the difference values remains constant. Note the R_{H –JBP – H} – R_{H – JU4U5 – H} does not approach a constant value at high concentration of KCl. Above 5 mM MgCl₂ the H-JU₄U₅-H construct is 3 Å shorter than the base paired construct. This value is close to the height contributed by one base pair (2.8 Å) to an A-form RNA duplex.