DNA MICROHETEROGENEITY & BENDING

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We have previously proposed a structural model for B-DNA with considerable conformational microheterogeniety in which certain segments adopt "butter fly" or "rhombic" motifs. To confirm our proposal, we are determining the structure of three oligomers in solution by NMR spectroscopy. For the first oligomer, we have recorded and analyzed the following spectra: 3 'P-'H heteroTOCSY, homoTOCSY, ECOSY, PECOSY, `P decoupled, H2/H2'' suppressed J scaled DQF, 'H-"P COSY, 'H_31 P GHSQC, 'H-"C HSQC and NOESY in water and D20 at several mixing times. We have been able to assign all the 'H resonances. In addition the 20 phosphorus atoms were assigned by a walk through the hetero 'H_3 'P TOCSY. We have also assigned all the sugar and backbone carbon atoms in the 13 C HSQC. Thus, we have a complete description of the sugar phosphate backbone of the 22 individual residues of the AAA duplex.