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Ultraviolet dichroic ratio of DNA from T2 and T5 bacteriophages
Author(s) -
Gray Donald M.,
Rubenstein Irwin
Publication year - 1968
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1968.360061107
Subject(s) - dichroic glass , chemistry , wavelength , dna , analytical chemistry (journal) , ultraviolet , dichroism , crystallography , optics , chromatography , physics , biochemistry
The dichroic ratios of T5st‐O and T2H bacteriophage DNA molecules were measured throughout the ultraviolet region of the spectrum. Two methods of DNA orientation were studied: ( 1 ) orientation in solution in a Shimadzu flow dichroism instrument attached to a Beckman DU spectrophotometer, and ( 2 ) alcohol precipitation of the DNA from solution and orientation in a thin film on the quartz face of a humidity chamber. Spectra in the latter case were recorded using a Gary Model 14 spectrophotomcter fitted with Glan prisms. The lower wavelength limit was 215 mμ in both systems. The DNA preparations were carefully characterized as to spectral purity, sedimentation coefficient, hyperchromicity, protein content, and DNA content. In addition, the structure of the DNA oriented in films was inferred from x‐ray diffraction patterns of fibers of the precipitated DXA. The A and B configurations of DNA in films could not be distinguished by the dichroic ratio measuiements. The dichroic ratio obtained for the film‐oriented DNA at high relative humidity shows the same wavelength dependence as for the flow‐oriented DNA. The same wavelength dependence for DNA in the fibrous state and in solution, when considered together with the x‐ray diffract ion results, indicates that DNA in solution maintains an orientation of bases which is similar to that in fibers. I 1 Or both solutions and films of DNA, the dichroic ratio is constant from 290mμ to 240 mμ and increases at wavelengths below 240 mμ. The increased parallel absorption below 240 mμ is consistent with the existence of an n →π* transition. The inherent molecular dichroic ratio is found to be the same for T5st‐O DNA and T2H DNA in solution, and is a maximum of 0.09 ± 0.02 at 260 mμ.