Preparation of subviral particles from vaccinia virions irradiated with ultraviolet light.

Nucleoprotein complexes, containing proteins covalently bound to DNA, were prepared from vaccinia virions irradiated with ultraviolet light. In the electron microscope, these complexes were observed to have a spherical morphology with a densely staining central portion, apparently containing proteins cross-linked to DNA, from which loops or fibers of DNA or DNA complexed with protein emerged.