Melting and premelting phenomenon in DNA by laser Raman scattering

Abstract

SynopsisRaman spectra of DNA from calf thymus DNA have been taken over a wide range of temperatures (25'-9.5') in both D20 and H,O. A study of the temperature dependence of the Raman spectra shows that the temperature profiles of the intensities and frequencies of the various bands fall into four different categories: 1) base bands that show a reversible increase in intensity prior to the melting region, i.e., a definite premelting phenomenon; 2) base bands that show little or no temperature dependence, 3) deoxyribose-phosphate backbone vibrations that show no temperature dependence up to the melting region, at which point large decreases in intensity occur; and 4) slow frequency changes in certain in-plane vibrations of guanine and adenine due to deuteration of the C-8 hydrogen of these purines in DZO.Certain Itaman bands arising from each of the four bases, adenine, thymine, guanine, and cytosine have been found to undergo a gradual increase in intensity prior to the melting region at which point large, abrupt increases in intensity occur. The carbonyl stretching band of thymine, involved in the interbase hydrogen bonding actually undergoes both a gradual shift to a lower frequency as well as an increase in intensity. These changes provide evidence that some change in the geometry of the bases relative to each other begins to occur around 5073, well below the melting region of 70"-8.i°C.From the spectra taken at various temperatures, the IINA appears to remain in the B conformation until the melting point is reached, at which time the 1)NA progresses into a disordered random-coil form. No A-form conformation is found either in the premelting or the melting region.

Raman spectroscopy of DNA packaging in individual human sperm cells distinguishes normal from abnormal cells

“…The 728 cm À1 adenine vibrational band is slightly enhanced in the sperm head, which indicates that adenine in the sperm cell is somewhat unstacked. This feature is very similar to that obtained in the Raman spectrum of a DNA melting process, which is characterized by a helix to coil transition [43]. This is in good agreement with an earlier Raman study of artificial protamine-DNA complexes [40].…”

Nucleosome conformation: pH and organic solvent effects

“…Among these are the line at 832 cm I which is assigned to a vibration of the phosphodiester group, and the line near 675 cm 1which is actually composed of an overlapping pair (doublet) of lines at 671 and 681 cm 1, due, respectively, to ring vibrations of thymine and guanine residues (10,(15)(16)(17)(18). At higher spectral resolution than employed for the present study, the doublet is more clearly resolved into its two components (see, for example, refs.…”

Structural and Energetic Considerations of Wave Propagation in DNA

“…First detected in oriented fibers of Na DNA at 75% relativ~ humidity by X-ray diffraction (Franklin and Gosling, 1953), the transition has·also been observed in 70-80% Ivanov et al, 1973Girod· et al, 1973;Erfurth and Peticolas, 1975;Herbeck et al, 1976). The transition occurs over a very narrow range ···of humidity and ethanol-water concentrations and is therefore highly cooperative.…”