Structural Polypeptides of Simian Virus 40

Abstract

To determine the number and molecular weights of the structural polypeptides of simian virus 40, we have analyzed purified virus by electrophoresis on 14% polyacrylamide gels containing sodium dodecyl sulfate. Full virus purified by several different methods showed six distinct bands with molecular weights of approximately 43,000 (VP1, containing 70% of virion protein), 32,000 (VP2, 9%), 23,000 (VP3, 10%), 14,000 (VP4, 6%), 12,500 (VP5, 4%), and 11,000 (VP6, 3%) both by analysis of radioactively labeled virions and by visualization of the polypeptide bands after staining. “Empty” virions contain decreased amounts of VP4, 5, and 6. The approximate molecular ratios of the polypeptides were 6.0, 1.0, 1.5, 1.5, 1.1, and 1.0. When virus degraded in an alkaline buffer was analyzed by velocity centrifugation in sucrose gradients, the two larger polypeptides (VP1 and VP2) remained at the top of the gradient, whereas the three smallest polypeptides (VP4, 5, and 6) sedimented as a complex with the viral deoxyribonucleic acid. VP3 was found in association with either VP1 and 2 or VP4, 5, and 6, depending on the conditions of degradation. Presumably, VP1 and VP2, comprising about 80% of the protein, form the capsid of the virus. VP4, 5, and 6 may form a nucleoprotein in the virion, and VP3 may serve as an intermediate structural component.