ION CHANNELS INDUCED IN LIPID BILAYERS BY SUBVIRION PARTICLES OF THE NONENVELOPED MAMMALIAN REOVIRUSES

Mechanisms by which nonenveloped viruses penetrate cell membranes as a n early step in infection are not well understood. Current ideas about the mode for cytosolic penetration by nonenveloped viruses include (i ) formation of a membrane-spanning pore through which viral components enter the cell and (ii) local breakdown of the cellular membrane to p rovide direct access of infecting virus to the cell's interior. Here w e report that of the three viral particles of nonenveloped mammalian r eoviruses: virions, infectious subvirion particles, and cores (the las t two forms generated from intact reovirus virions by proteolysis), on ly the infectious subvirion particles induced the formation of anion-s elective, multisized channels in planar lipid bilayers under the exper imental conditions used in this study. The value for the smallest size conductance varied depending on the lipid composition of the bilayer between 90 pS (Asolectin) and 300 pS (phosphatidylethanolamine:phospha tidylserine) and was found to be voltage independent. These findings a re consistent with a proposal that the proteolytically activated infec tious subviral particles mediate the interaction between virus and the lipid bilayer of a cell membrane during penetration. In addition, the findings indicate that the ''penetration proteins'' of some enveloped and nonenveloped viruses share similarities in the way they interact with bilayers.