Studies of the early events of the replicative cycle of three variants of Mengo encephalomyelitis virus in mouse fibroblast cells

Abstract

The early events in the replicative cycle of three variants (L, M, and S) of Mengo encephalomyelitis virus were studied in the mouse fibroblast cell, strain L. The three variants were found to differ with respect to both the rate of attachment and the amount of virus capable of attachment to L cells. Of the three variants, S-Mengo was shown to attach most rapidly and L-Mengo least rapidly. The kinetics of attachment of each variant, as calculated from measurements of adsorption of both infectivity (PFUs) and radioactivity (32PO4-labeled virus), were similar at 0° and 37°, and 20%, 85%, and 95% of L-, M-, and S-virions, respectively, attached to L cells under the conditions employed. Virus penetration, measured as the rate at which attached virus became resistant to neutralization by Mengo antiserum was found to occur very rapidly-more than 70% of adsorbed virus penetrates by 40 minutes-and the rates of penetration of the three variants were identical. Studies of the uncoating of the three variants revealed that M-virions are uncoated more rapidly than are L- and S-virions. This observation is consistent with the earlier finding that the eclipse phase of the M-variant is 1.5 hours shorter than that of either the L- or S-variant. Inhibition of protein synthesis does not affect either the rate or the extent of the uncoating of any of the variants. The data obtained show that both infectious and noninfectious particles of all three variants attach, penetrate, and are uncoated in the L cell. Thus, the high particle/PFU ratios of the variants cannot be explained by the inability of noninfectious virions to complete the early events of the replicative cycle. © 1970.