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Circular dichroism of superhelical DNA
Author(s) -
Maestre Marcos F.,
Wang James C.
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.360100608
Subject(s) - chemistry , dna , circular dichroism , crystallography , ionic strength , molecule , helix (gastropod) , biophysics , biochemistry , aqueous solution , biology , ecology , organic chemistry , snail
The circular dichroism (CD) spectra of a number of superhelical DNA's have been measured. The introduction of negative superhelical turns causes an increase in magnitude of the positive band around 280 mμ, while the trough around 250mμ is little affected. For two samples of λb2b5c DNA (20 Mdalton) containing different number of negative superhelical turns, the magnitude of the positive band relative to that of the nicked control increases with increasing number of superhelical turns. In 2 M NaCl, the small (1.45 Mdalton) superhelical DNA from E. coli 15 shows an unusually large difference in CD compared with that of the same DNA with a few single‐chain scissions per molecule. This large difference is not observed in a medium containing p. 0.11 M NaCl. These results indicate that the double helix in a superhelical DNA is perturbed somewhat due to the bending and torsional forces in such a molecule. The magnitude of such structural alteration seems to depend on the number of superhelical turns per unit length, the size of the DNA molecule, as well as the ionic medium.