Biophysical Journal 55: 1237-1249 (1989)
© 1989 the Biophysical Society

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Low angle light scattering studies on whole, half, and quarter molecules of T2 bacteriophage DNA.

Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106.

ABSTRACT

Static light scattering measurements have been made at angles as low as 8 degrees on whole, half, and quarter molecules of native, T2 bacteriophage DNA in 0.195 M Na+. The fragments were obtained by high-speed stirring of the native DNA, and fractionated on methylated-albumin-kieselguhr columns. Accompanying measurements of sedimentation coefficients and intrinsic viscosities were made. Because linear extrapolations of light scattering data above 8 degrees for these samples were suspect, the measurements were analyzed by fitting curves calculated from the theory of wormlike coils to experimental curves at c = 0. Results showed that the excluded volume parameter, epsilon, must be used in analyzing the scattering curves; a reasonable value of epsilon was 0.08, in agreement with that found for T7 DNA (Harpst, J. A. 1980. Biophys. Chem. 11:295-302). The persistence length of all three DNAs in this paper was 50 +/- 5 nm, showed no dependence on molecular weight, but was somewhat below that reported previously for T7 DNA (60 nm). Theoretical curves calculated with the preceding parameters had a clear upward curvature in scattering envelopes below 8 degrees for quarter and half molecules, but such curvature was minimal for whole T2 DNA, so that linear extrapolations of experimental data above 8 degrees gave a molecular weight and root-mean-square radius which were nearly the same as those from theory. The molecular weight and radius for whole T2, derived from the comparison of theory and experiment, were 115 X 10(6) and 1,224 nm, respectively. The measurements on T2 DNA were clearly at the upper limit of current techniques.

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