BASE DEPENDENCE OF B-DNA SUGAR CONFORMATION IN SOLUTION AND IN THE SOLID-STATE

Analysis of H-1-NOESY solution data for eight short DNA duplexes has r evealed pronounced differences between the sugar conformations of puri ne and pyrimidine nucleotides. It was found that the H1'-H4' interprot on distance is less than ca. 3.0A in pyrimidine sugars, while in purin e sugars it is more than ca. 3.0A This difference has been analyzed by comparison with the sugar conformations of highly resolved B-DNA crys tal structures and model sugar conformations. The conclusion can be dr awn that the deoxyribose conformation is of the general C2'-endo type but pyrimidine sugars are characterized by smaller phase angles of pse udorotation P (90 degrees < P < 150 degrees), while purine sugars have larger P values that are greater than ca. 140 degrees (140 degrees < P < 180 degrees). There is no such clear base dependence of sugar conf ormation in highly resolved B-DNA crystal structures; however the simi lar trend can be seen as in the solution studies. Based on B-type DNA crystal structures, J-coupling constants have been calculated, and the applicability of experimental coupling measurements to the determinat ion of sugar conformation is discussed.