Figure 1.

(a) Temperature dependence of termination probability P for phage λ terminator tR2 reported by Wilson and von Hippel (15). +, □, and × denote the probabilities to terminate 7, 8, and 9 nt downstream from the beginning of the poly(T) stretch. The sum is shown as ⋄. (b) +, □, and × above divided by ⋄ to make a branching fraction f. (c) Comparison of ionization model Eq. 1 with ⋄ from A. The ionization energy has been fit to ɛ₀ = 0.7 eV (16 kcals/mole; 1 cal = 4.18 J) and the quantity n/M^3/2 adjusted to make the curves match at 30°C. (d) Prediction of Eq. 1 for dependence on Mg²⁺ concentration compared with data of Reynolds et al. (7).