DISTANCE MEASUREMENTS IN NUCLEIC-ACIDS USING WINDOWLESS DIPOLAR RECOUPLING SOLID-STATE NMR

A windowless, homonuclear dipolar recoupling pulse sequence (DRAWS) is described and a theoretical basis for describing its recoupling perfo rmance is developed using numerical techniques. It is demonstrated tha t DRAWS recouples weak dipolar interactions over a broad range of expe rimental and molecular conditions. We discuss two spectroscopic contro l experiments, which help to take into account effects due to insuffic ient proton decoupling, relaxation, and static dipolar couplings to ne arby C-13 spins at natural abundance. Finally DRAWS is used in combina tion with selective C-13 labeling to measure C-13-C-13 distances in fi ve doubly labeled DNA dodecamers, [d(CGCGAATT*CGCG)](2), which contai n the binding site for the restriction enzyme EcoRI, The longest dista nce reported is 4.8 Angstrom. In most cases the distances agree well w ith those derived from X-ray crystallographic data, although small cha nges in hydration level can result in relatively large changes in inte rnuclear distances.