Fig. 2.

Phosphorylation stabilizes Ets-1. (a) The CD spectra of ΔN244 and ΔN244^5p are essentially superimposable, indicating that phosphorylation does not alter the secondary structure of the Ets-1 fragment. (b) Signal averaged CD spectra of ΔN244 and ΔN244^5p recorded with increasing temperature in 10°C intervals. ΔN244 had a midpoint unfolding temperature of ~ 55 °C, whereas ΔN244^5p remained well folded at 90 °C. (c) Urea denaturation of ΔN244 versus ΔN244^5p in the presence of 50 mM, 100 mM, and 500 mM KCl. Lines show the data fit (see Methods). Phosphorylation elevated the [urea]_1/2 from ~4.8 M to ~5.6 M in 50 mM KCl. Increasing ionic strength reduced the co-operativity of ΔN244 unfolding, but did not markedly change the stability of ΔN244^5p. Samples were in 25 mM potassium phosphate, pH 7.9, and 100 mM KCl at 25 °C unless stated otherwise.