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Precollapse of T7 DNA by spermidine at low ionic strength: A linear dichroism and intrinsic viscosity study
Author(s) -
Baase Walter A.,
Staskus Paul W.,
Allison Stuart A.
Publication year - 1984
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.360231210
Subject(s) - spermidine , chemistry , circular dichroism , counterion , ionic strength , dna , counterion condensation , persistence length , random coil , viscosity , particle (ecology) , dna condensation , condensation , crystallography , chemical physics , thermodynamics , organic chemistry , biochemistry , polymer , physics , ion , enzyme , oceanography , transfection , aqueous solution , gene , geology
At low salt ([Na + ] = 10 −3 M ), spermidine is capable of transforming DNA from a highly extended random coil to a compact particle. The transition takes place at a spermidine concentration of around 25 μ M and the compact particle has been previously studied in considerable detail for several different DNAs. The objective of the present study is to see what effect, if any, spermidine has on T7 DNA conformation prior to collapse using flow dichroism and intrinsic viscosity. We conclude that increasing the spermidine concentration from 0 to the collapse transition point (above 20 μ M ) makes DNA increasingly nondraining. Furthermore, the persistence length dropped from 785 (±42) to 560 (±32) to 445 (±26) Å on increasing the ambient spermidine concentration from 0 to 1 to 10 μ M . These results are in good agreement with counterion condensation theory and Odijk's theory of the electrostatic contribution to the persistence length of DNA. Nonetheless, it is concluded that counterion condensation is not entirely responsible for DNA collapse and that crosslinking promotes the transition to the compact state.