Biogenesis of poxviruses: Further evidence for inhibition of host and virus DNA synthesis by a component of the invading inoculum particle

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The effect of virion-derived pH 7.8 DNase on the host DNA replication was further studied. DNA polymerase(s) active with exogenous single-stranded (ss) and double-stranded (ds) DNA templates were monitored in nuclear, large particulate and supernatant cytoplasmic fractions from control and infected cells. Infection suppressed the nuclear ds activity appreciably but had little effect on the ss one, regardless of prevailing RNA and protein synthesis. By contrast, both the cytoplasmic supernatant DNA polymerase activities were elevated after infection and this stimulation depended upon ongoing protein synthesis. Kinetics of the polymerizing reaction, followed in pulse-chase experiments revealed that nascent DNA in the controls was conserved while in the infected nuclei it became degraded. The degradation products were characterized by paper chromatography and shown to be predominantly low molecular weight polynucleotide chains less than 2–8 nucleotides long. A DNase activity with characteristics of the virion-associated DNase was detected in infected nuclei at about the same time as host DNA synthesis was affected. Inhibition of DNA synthesis by a factor originating from the virus was also demonstrated on the cytoplasmic vaccinia DNA replication by superinfection with vaccinia under appropriate circumstances. As a whole these observations imply that the ss DNA being formed is the most likely site of action of the nuclease originating from the penetrating virion core and lends further support to the notion that the DNase from the invading virus is responsible for inhibiting host DNA synthesis.