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The viscometric behavior of native and relaxed closed circular phage pm 2 dna at intermediate and high ethidium bromide concentrations

Biopolymers 16(6): 1343-1356

The viscometric behavior of native and relaxed closed circular phage pm 2 dna at intermediate and high ethidium bromide concentrations

The specific viscosity of closed circular [phage] PM2 DNA was measured in the presence of concentrations of ethidium bromide up to 5 mg/ml. Native viral PM2 DNA I and enzymatically prepared relaxed, closed circular PM2 DNA I0 exhibit a complex dependence of the specific viscosity on the extent of supercoiling. As the number of superhelical turns is increased in the positive sense from zero, the viscosity decreases to a minimum, then passes through a secondary maximum, and eventually again increases as the dye-induced duplex unwinding proceeds. In the case of DNA I, a corresponding behavior is mirrored in the negative sense as dye is removed from the principal viscometric maximum (complete relaxation of the DNA by dye). The shape of the curve relating specific viscosity to the extent of supercoiling is similar for superhelical DNA of either handedness, a result which indicates that the influence of any regions of special secondary structure (such as denatured loops) on the viscosity is minimal. At very high dye concentrations the specific viscosity decreases dramatically. This effect might arise from intermolecular aggregation or from a dye-induced collapse in the DNA secondary structure.

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Accession: 006792680

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