Chromatin-like structures obtained after alkaline disruption of bovine and human papillomaviruses

Four low-molecular-weight polypeptides migrating like H2a, H2b, H3, and H4 calf liver histones were detected by sodium dodecyl sulfate-acrylamide gel electrophoresis of highly purified preparations of bovine papillomavirus (BPV) and human papillomavirus (HPV). Complexes of these polypeptides and viral DNA were isolated by agarose-gel filtration of the alkaline disruption products of both viruses. When observed under the electron microscope, these complexes appeared as circular structures composed of nucleosomes with a diameter of about 8.0 nm interconnected by a naked DNA filament. The maximal frequency of nucleosomes per molecule was 30 for both viruses, corresponding to a condensation ratio of the viral DNA of 2.5.