Multiplicity activation of vaccinia virus in L cells

Multiplicity activation of herpes simplex virus in mouse neuroblastoma (C1300) cells

The virus yields and number of infectious centres of HSV infected mouse neuroblastoma C1300 cells (clone 41 A3) infected at different multiplicities of infection (MOI) were found to vary more than the differences of HSV concentrations of the virus suspensions used for infection of the cells. This suggested that a C1300 cell had to be infected with more than one HSV particle in order to produce progeny virus-multiplicity activation. The greater than expected enhancement of virus production of C1300 cell cultures receiving increasing MOI of HSV was probably not due to improved virus adsorption, nor influenced by non-virus factors in the virus inoculum stimulatory for HSV replication. A hypothesis, that the block in virus replication was promoted by an inhibitor of an HSV specified regulatory protein and could be overcome by the addition of HSV DNA copies in the infected cell, was by the results of two types of experiments. Presence of phosphonoformic acid, an inhibitor of the HSV specified DNA polymerase, in the culture medium of HSV infected permissive GMK cells resulted in non-linear relationships between virus yields and MOI. An HSV temperature sensitive mutant (ts B5), defective in a late structural protein, rescued wild type HSV in C1300 cells.

Partial reactivation of chlorine-treated echovirus

After treatment of a dispersed suspension of echovirus with HOCl, much of the lost plaque titer was restored if the treated virus was induced to aggregate by adjustment of the suspending medium to pH 4.5. This did not appear to be a repair of individual virions but rather a special kind of multiplicity-related increase in plaquing efficiency which occurred when the host cell received several of the damaged virions in a clump.

Spectrum of physical properties among the virions of a whole population of vaccinia virus particles

Populations of virions released from cultures of L cells infected with vaccinia virus are composed of particles which differ substantially from each other in sedimentation rate and buoyant density. Clumps of two and three virions sediment enough faster than single particles so that fractions containing only singles and others with predominantly pairs can be isolated. The observed velocity range for single particles is much greater than that attributable to diffusion and convection in the centrifuge. Plaquing efficiency is three times higher in a small fraction of the slowest-moving virions than in the major part of the population, even though no size difference can be seen in the electron microscope. Isopycnic densities in potassium tartrate range from 1.15 to 1.23, enough to account for the observed range in velocities. Centrifugation was done in the BXIV zonal rotor at very low virion concentration (less than 10(8) per ml at any point in the spectrum). Virus count and state of aggregation were determined by electron microscopy.