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Dehydrated circular DNA: Circular dichroism of molecules in ethanolic solutions
Author(s) -
Gray Donald M.,
Taylor Thomas N.,
Lang Dimitrij
Publication year - 1978
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.1978.360170111
Subject(s) - chemistry , covalent bond , dna , circular dichroism , dna supercoil , molecule , ethanol , crystallography , ammonium acetate , polynucleotide , analytical chemistry (journal) , stereochemistry , chromatography , organic chemistry , biochemistry , dna replication , high performance liquid chromatography
We have measured the ultraviolet CD spectra for covalently closed and linear forms of phage PM2 DNA in solution. We find that increased concentrations of salt or ethanol (up to 50% ethanol by weight) depress the long‐wavelength positive CD bands in the spectra of both forms of DNA, although the spectrum of the native covalently closed DNA always has a slightly larger magnitude of these bands than does the spectrum of the linear DNA. In addition, both DNAs are equally capable of undergoing a transition to the A conformation in 70–80% ethanol at low Na + concentrations. Thus, the constraint imposed by the covalent closure of a DNA molecule does not seem to hinder its conformational response to these changing solution conditions. Lang [(1973) J. Mol. Biol. 78 , 247–254] has found by electron microscopy that T7 DNA has an inherent ability to condense into compact particles, suggested to be supercoils of multiple order. Both covalently closed and linear forms of PM2 DNA also become condensed when the DNA, in 0.2 M ammonium acetate and 1 m M EDTA, is exposed to ethanol and subsequent drying on specimen grids [Lang, D., Taylor, T. N., Dobyan, D. C. & Gray, D. M. (1976) J. Mol. Biol. 106 , 97–107]. Under similar conditions, in solutions of 0.2 M ammonium acetate and 1 m M EDTA to which ethanol is added, we have measured the CD spectra of both covalently closed and linear forms of DNA. Below ethanol concentrations at which the DNA obviously precipitates, the CD spectra of both forms have reduced long‐wavelength positive CD bands.