FIGURE 4.

Effect of monovalent cation concentration on the initial rate of HPR1 circularization at −8°C. Solutions of linear, internally ³²P-labeled HPR1 containing the indicated salts in the presence of 1 mM Tris-EDTA at pH 8.0, were rapidly frozen, then incubated for 10 min at −8°C and analyzed as in Figure 3 ▶. (A) Stimulatory effect of Na⁺ ions tested either in the form of Na₃EDTA at pH 8.0 (▴) or Na-APB at pH 8.0 (▪), where APB is the universal buffer mixture of acetate, phosphate, and borate. (B) Inhibitory effect of Tris-HCl at pH 8.0 in the presence of either 30 mM Na₃EDTA at pH 8.0 (▴) or 100 mM LiCl (▪).