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Magnetic circular dichroism study on synthetic polynucleotides, bacteriophage structure, and DNA's
Author(s) -
Maestre Marcos F.,
Gray Donald M.,
Cook Randall B.
Publication year - 1971
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.360101214
Subject(s) - chemistry , polynucleotide , hyperchromicity , circular dichroism , polymer , crystallography , spectral line , dna , magnetic circular dichroism , stacking , nuclear magnetic resonance , physics , biochemistry , organic chemistry , astronomy
The MCD (magnetic circular dichroism) spectra of Ap, ApA, ApApA, poly A, Up, UpU, poly U and double‐stranded poly A:U alternating copoly A–U and alternating deoxyribopoly A–T were measured with a Cary 61 spectropolarimeter fitted with a Varian superconducting magnet at a field strength of 50 Kgauss. The MCD spectra of T2 and T5 DNA at various stages of heal denaturation were measured as a function of hyperchromicity of the sample. MCD spectra of the intact and degraded T2 and T5 phages were used to study the degree of alteration of the DNA inside the phages versus the DNA in vitro. The results for the adenine polymers show that the main MCD bands, B 2u (271 nm), B 1u (252 nm), and E 1u (212 nm), show a decrease in specific magnitude as the length of the polymer is increased, reflecting the degree of stacking of the polymer. In contrast, the uridine series of polymers shows little change of the MCD bands, indicating that there is little interaction between the bases regardless of the length of the polymers. The MCD spectra of poly A:U, alternating poly r(A–U): (A–U), and alternating poly d(A–T):(A–T) show significant differences among themselves in the magnitude of the B 2u band and when compared with the sum of the spectrum for the poly A plus poly U. This may indicate the selective effect of hydrogen bonding on the B 2u band. Alternatively, the difference may be due to the absence of an n → π* transition in the double‐stranded polymer. Measurements of denatured T2 and To DNA's show increases in all MCD bands. The T2 DNA internally packed in phage shows an increase of the B 2u and E 1u bands, the B 2u remaining unchanged. The internal T5 DNA shows an increase of the B 1u band only. Thus, the internal DNA structure is altered in a manner quite different from a simple denaturation caused by hydrogen bond breaking. Furthermore, different MCD bands indicate that different modes of DNA packing exist for T2 and T5 phages.