Viral Ribonucleic Acid Synthesis by Newcastle Disease Virus Mutants Isolated from Persistently Infected L Cells: Effect of Interferon

Abstract

The synthesis of different viral ribonucleic acid (RNA) species was studied in chick embryo (CE) and mouse L-cell cultures infected with the Herts strain of Newcastle disease virus (NDV o ) and a mutant isolated from persistently infected L cells (NDV pi ). In CE cell cultures, both viruses synthesized significant amounts of 54, 36, and 18 S RNA. However, in L cells, synthesis of 54 S virion RNA was markedly reduced. From these results, it seems likely that the low yield of infective virus in L cells is due to a deficient synthesis of 54 S RNA in this host. On this basis, however, it is apparent that the “covert” replication of NDV o in L cells is due to factors other than viral RNA synthesis. When low concentrations of interferon were used to pretreat CE cells, a differential effect on the synthesis of various RNA species was observed. The 18 S RNA of NDV o was more sensitive to interferon action than the 36 and the 54 S RNA species. In contrast, the 18 S RNA of NDV pi was less sensitive than the 36 S and the 54 S RNA. The inhibition of 54 S RNA synthesis correlated with the reduction of viral yield and explained the greater sensitivity of NDV pi to interferon.