Figure 1.

Condensation of ¹⁵NH₄⁺ ions around DNA. (A) 1D ¹⁵N spectra recorded at 25˚C for solutions of the Antp HD (magenta) and the 15-bp DNA (black), each of which was equilibrated with the buffer shown in the green box. A ¹⁵N spectrum recorded for the buffer alone is also shown (green). (B) ¹⁵N NMR signals from ¹⁵NH₄⁺ ions at different concentrations of the Antp HD and the 15-bp DNA. (C) Differences in the ¹⁵N chemical shift of ¹⁵NH₄⁺ ions in the presence of various concentrations of the 15-bp DNA. (D) Total concentrations of ¹⁵NH₄⁺ ions in the DNA or protein solutions after buffer equilibration. Each concentration was determined using the ratio of ¹⁵N NMR signal intensity of ¹⁵NH₄⁺ to the intensity of the ¹⁵N formamide signal.