RESUMEN
Four methods for preparation of Shope papilloma virus have been compared. These comprise: (1) alternate centrifugation at low and high speed after grinding with alundum and saline, (2) purification with a fluorocarbon after similar extraction, (3) extraction with the aid of 2-mercaptoethanol and purification by alternate low- and high-speed centrifugation, and (4) extraction with 2-mercaptoethanol followed immediately by centrifugation to equilibrium in CsCI. It is necessary to remove CsCI before chemical analysis, and this has been accomplished by chromatography on Sephadex G-75. After banding, the virus from preparation (4) appears homogeneous in the electron microscope. The deoxyribonucleic acid (DNA) contents of the preparations were (1) 7.8, (2) 8.3, (3) 8.0, and (4) 11.9 percent of total nucleoprotein. At equal inputs of DNA, there was no significant difference in infectivity of any of the preparations. Method (4) is simpler than the others and results in a higher yield of a homogeneous preparation.