Hydrodynamic determination of molecular weight, dimensions, and structural parameters of Pf3 virus

Measurements of the translational, DT, and rotational, DR, diffusion coefficients of Pf3 virus by low-angle polarized intensity fluctuation spectroscopy and field-free transient electric birefringence, respectively, give a length of 720 +/- 25 nm and diameter of 6.5 +/- 1.5 nm upon simultaneous solution of the Broersma equations for rigid rods. Sedimentation coefficient and density increment values obtained under solvent conditions identical with those of DT give a molecular weight of (13.4 +/- 0.8) x 10(6) g mol-1, which gives a mass per length of 18 600 +/- 1300 g mol-1 nm-1. Combining these results with the molecular weight of Pf3 DNA yields a number of protein subunits of 2500 +/- 160 and 2.38 +/- 0.14 nucleotides/protein subunit. Sedimentation coefficient and density increment values of Xf virus when combined with a value for the Xf translational diffusion coefficient [Chen, F. C., Koopmans, G., Wiseman, R. L., Day, L. A., & Swinney, H. L. (1980) Biochemistry 19, 1373] yield a molecular weight of (17.9 +/- 1.0) x 10(6) g mol-1, a number of protein subunits of 3590 +/- 230, 2.07 +/- 0.15 nucleotides/protein subunit, and a mass per length of 18 300 +/- 1200 g mol-1 nm-1. Thus, despite major differences in the DNA-protein packing between these viruses, as well as fd virus, the mass per lengths are surprisingly similar.