Structure of a psoralen cross-linked DNA in solution by nuclear magnetic resonance.

One- and two-dimensional nuclear magnetic resonance (NMR) methods were used to determine a three-dimensional model of an eight-base-pair DNA fragment (d-GGGTACCC) cross-linked with psoralen in solution. Two-dimensional nuclear Overhauser effect experiments were used to assign the spectrum and estimate distances for 171 proton pairs in the cross-linked DNA. The NMR-derived model shows a 53 degree bend into the major groove that occurs primarily at the site of drug addition and a 56 degree unwinding that spans the eight-base-pair duplex.