POLYNUCLEOTIDES .23. A UV RESONANCE RAMAN-STUDY OF D(A(-G)(10), A SINGLE-STRANDED HELIX WITHOUT STACKED OR PAIRED BASES())

UV resonance Raman spectroscopy has been utilized to directly observe structural features of the recently described nucleic acid single-stra nded helix d(A(+)-G)(10). An absence of base stacking is confirmed by invariant hypochromic ratios of dominant vibrational modes for the oli gomer relative to its constituent monomers as the structure is thermal ly denatured. The N-1 of dA residues is protonated, as determined by s imilarity to the ring-stretching vibrations for protonated adenine and its derivatives. Selective resonance enhancement of Raman vibrational modes from dA and dG residues shows frequency shifts upon thermal den aturation that confirm the participation of the exocyclic amino of dA but not dG residues in H-bonding. Conformationally sensitive glycosyl bond modes suggest anti residue conformations.