Early events in polyoma virus infection: attachment, penetration, and nuclear entry

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Abstract
The plaque-assay technique was used to determine the optimal conditions for adsorption of polyoma virions to host cells. [Mouse embryo BALB/3T3, polyoma virus transformed mouse embryo Py-3T3, baby hamster kidney BHK-21, polyoma virus transformed baby hamster kidney Py-BHK, primary mouse embryo and baby mouse kidney cells were used.] Using these optimal conditions of adsorption, an EM study of the early events of infection was performed. EM and autoradiography demonstrated that the viral coat proteins and DNA arrive simultaneously in the nucleus as early as 15 min postinfection. When horseradish peroxidase-labeled virions, pseudovirions and capsids were used to infect cells, only the particles with nucleic acid or a factor(s) associated with the nucleic acid, i.e., histones, appeared to enter the nucleus. When virions were used to infect either permissive or nonpermissive cells, identical early events of viral infection, i.e., adsorption, penetration and nuclear transport, were observed, suggesting that these early events of infection are a property of the virion and not the host cell.