Structure of bacteriophage T7. Small-angle X-ray and neutron scattering study.

Small-angle x-ray and neutron scattering techniques were applied to bacteriophage T7 solutions at different scattering densities. Scattering curves determined under a variety of experimental conditions were used to derive a set of parameters characterizing the shape, size, and weight of the whole phage particle and of its DNA and protein components. The T7 head has an icosahedral shape with an edge of 37.7 +/- 0.5 nm, a volume of (12.0 +/- 1.0) x 10(4) nm3, and a small tail amounting to 6--7% of the head volume. The intraphage DNA region is most probably a hollow sphere. The best fit to the data was obtained with a model in which the hollow sphere filled with a protein core with a diameter of 24 nm. The average degree of swelling (i.e., the ratio of the hydrated to the dry volume) of the particle is 2.3; the degree of swelling of the DNA component is higher, 3.2, and that of the protein part is lower, 1.2.