Crystal structure of O4-methyl uridine: stacking induced changes in the geometry of the pyrimidine ring and its mutagenic role.

The geometric properties of the pyrimidine ring of O4-methyl uridine more closely resemble those of cytidine than diketo uridine. Differences between the independent molecules of O4-methyl uridine are observed in the C(7)-O(4)-C(4)-C(5)-C(6) bond orders and the planarity of the pyrimidine rings. These differences are attributed to the monopole-induced dipole interactions between the ribose ring oxygen atom and a neighboring base of molecule A. A survey of the literature reveals that similar stacking-induced effects occur in other structures, involving both pyrimidine and purines. Finally, two base pairing schemes between O4-methyl uridine and guanosine, in which two hydrogen bonds can form, have been presented. Of these two the mispair with Watson-Crick geometry is favored.