SynopsisOriented fibers drawn from aqueous gels of calf-thymus DNA were maintained at constant relative humidities of 75 and 92% to yield canonical A-DNA and B-DNA structures, respectively. Raman spectra of the two forms of DNA were recorded over the spectral range KKL4OOO cm-l. The authenticated DNA fibers were deuterated in hygrostatic cells containing DzO at appropriate relative humidities, and the corresponding spectra of deuterated DNAs were also obtained. The spectra reveal all of the Raman scattering frequencies and intensities characteristic of A-and B-DNA structures in both nondeuterated and deuterated forms, as well as the frequencies and intensities of adsorbed solvent molecules from which the hydration content of DNA fibers can be calculated. Numerous conformation-sensitive vibrational modes of DNA bases and phosphate groups have been identified throughout the 300-1700-~m-~ interval. Evidence has also been obtained for conformation sensitivity of deoxyribosyl CH stretching modes in the 2800-3000-~m-~ region. Raman lines of both the backbone and the bases are proposed as convenient indicators of A-and B-DNA structures. The results are extended to Z-DNA models investigated previously. Some implications of these findings for the determination of DNA or RNA structure from Raman spectra of nucleoproteins and viruses are considered.

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Laser Raman spectroscopy indicates that the inner histones which are bound to DNA in chromatin or in isolated nu bodies are similar in conformation to the inner histones which are dissociated from DNA in high-salt solutions. This structure contains, on the average, 51+/-5% alpha-helix and no substantial beta-sheet conformation. It is proposed that the protein core of the nu body has a high alpha-helix content.

The cyclopentadecapeptide, c(VPGVG)3, a model structure for protein type‐II β‐turns [W. J. Cook et al. (1980) J. Am. Chem. Soc. 102, 5502–5505], has been investigated by laser Raman spectroscopy. Data obtained from both normal and deuterated crystals identify amide I, III, I′, and III′ bands characteristic of the β(II)turn. The structurally related polypentapeptide poly(VPGVG) in normal and deuterated forms has also been investigated, and exhibits the same Raman amide bands as c(VPGVG)3. The coacervate of poly(VPGVG), obtained by heating the solution to 40°C, likewise exhibits a Raman spectrum very similar to that of the c(VPGVG)3 crystal. Raman spectra thus indicate closely similar secondary structures for crystalline c(VPGVG)3 and aqueous poly(VPGVG), and provide an empirical basis for interpreting the conformation sensitive amide bands of globular proteins in terms of β(II)turn structures that may be present. An important conclusion from the present findings is that the amide I Raman profile of a protein may not be sufficient in general to distinguish turns from helix and sheet secondary structures, since the major amide I peaks of the β(II)turn at 1676 and 1652 cm−1 overlap, respectively, with amide I profiles generated by β‐sheet and α‐helix conformations.

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