Proteolytic Cleavage of VP1 in 'A' Particles of Coxsackievirus B3 Does Not Appear to Mediate Virus Uncoating by HeLa Cells

Department of Microbiology and Immunology, Hahnemann Medical College, Philadelphia, Pennsylvania 19102, U.S.A. ‘A’ particles of Coxsackievirus B3 were generated from native virus by heating and purified by sucrose gradient centrifugation. These particles were found to be similar to ‘A’ particles formed by elution from cellular receptors of HeLa cells. Electrophoretic analysis of [ 35 S]methionine-labelled ‘A’ particles revealed that treatment of the particles with chymotrypsin resulted in the cleavage of VP1 and the formation of a cleavage product which migrated between VP2 and VP3. Analysis of the protease-treated material on sucrose gradients revealed a ribonuclease-sensitive particle which sedimented more slowly than an ‘A’ particle. This particle apparently degraded to release the viral RNA, thereby providing an in vitro model for protease-mediated uncoating of ‘A’ particles. The subviral particles of Coxsackievirus B3 were found to be immunoprecipitable with heterotypic Coxsackievirus group B antisera, thereby providing a method for the recovery of products produced in the cell early in infection. Infected cells which had been treated to remove unreacted virus were disrupted, and the lysates were reacted with heterotypic antisera. Analysis of the precipitated material revealed that no cleavage products were formed and no polypeptides were lost. Therefore, it appears that proteolysis is not involved in the uncoating of Coxsackievirus B3 in infected cells. Keywords: Coxsackievirus B3, virus uncoating, proteolysis of A particles Present Address: Laboratory of Molecular Virology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20205, U.S.A. Received 26 November 1980; accepted 13 March 1981.