Control of Viral RNA Synthesis in Eastern Equine Encephalitis Virus

The pattern of viral RNA synthesis and growth of a temperature- sensitive mutant (Ets-4) of eastern equine encephalitis (EEE) virus was compared with that of the parent. Growth of Ets-4 was moderately inhibited at 30 and 37 C compared with that of EEE, and was strongly inhibited at 42 C. In Ets-4, similar patterns of inhibitions were observed in the production of complement-fixing antigen and hemagglutinin (HA), which indicated that Ets-4 was defective in viral protein synthesis. The viral RNA synthesis induced by both virus in infected cells was studied extensively. The mutant produced three times as much total viral RNA as EEE virus at 37 C, but less infectious RNA (IRNA). Comparison of the specific infectivity (IRNA/total viral RNA) of the two viruses showed that of Ets-4 to be 0.1 that of the parent. RNA from each of the viruses was analyzed more completely with sucrose gradient centrifugation. Ets-4 at 37 C produced greater amounts of a noninfectious 20S species (double-stranded forms, ribonuclease-resistant) and a poorly infectious 27S form (single-stranded, ribonuclease-sensitive) of viral RNA. Production of single-stranded infectious species, 45S, of viral RNA by Ets-4 was less than that by EEE virus, but the total uptake of radioactive uridine was higher, suggesting that the 45S species of RNA synthesized in Ets-4 - infected cells was biologically defective. On the basis of the facts noted above, it appeared that viral RNA synthesis in Ets-4 - infected cells was out of control. Control appeared to be restored to the levels and pattern of the parent by superinfection with the parent EEE virus or VEE virus but not with others.