Molecular and crystal structure of deoxyguanosine 5′-phosphate

RECENT crystallographic studies of the dinucleosides ApU (ref. 1) and GpC (ref. 2) have given experimental proof for the base pairing arrangement proposed by Watson and Crick for the DNA double helix3. Another striking feature of this structure relates to the torsional angle about the C5′-C4′ bond in the phosphate–sugar backbone chain. In the Crick and Watson model4, this conformation is gauche–trans (GT). Crystal structures of 5′-nucleotides, dinucleosides and dinucleotides so far studied, however, have shown only the gauche–gauche (GG) conformation about this bond. The GG conformer is also the only one found in the refined models of the proposed structure of the double helical nucleic acids and polynucleotides5–7. The only nucleotide with a GT conformation is 6-azauridine-5′-phosphate8which is not a normal monomer unit of nucleic acids. It is also reported that 5′-dGMP assumes preferentially GT conformation in solution9.