BII nucleotides in the B and C forms of natural-sequence polymeric DNA: A new model for the C form of DNA

A combination of solid-state P-31 and C-13 NMR, X-ray diffraction, and mode l building is used to show that the B and C forms of fibrous macromolecular DNA consist of two distinct nucleotide conformations, which correspond clo sely to the BI and BII nucleotide conformations known from oligonucleotide crystals. The proportion of the BII conformation is higher in the C form th an in the B form. We show structural models for a 10(1) double helix involv ing BI nucleotides and a 9(1) double helix involving BII nucleotides. The 1 0, BI model is similar to a previous model of B-form DNA, while the 9(1) BI I model is novel. The BII model has a very deep and narrow minor groove, a shallow and wide major groove, and highly inclined bases. This work shows t hat the B to C transition in fibers corresponds to BI to BII conformational changes of the individual nucleotides. (C) 2000 Academic Press.