Altered viral ribonucleic acid synthesis by a temperature-sensitive mutant of eastern equine encephalitis virus

Abstract

A temperature-sensitive mutant (Ets-4) derived from eastern equine encephalitis virus induced the synthesis of unusually large amounts of viral RNA in infected chick embryo cells. Ets-4 produced two to four times more RNA at 37 °C; however, its yield of mature virus was about 10 times less than the parent virus. Viral RNA extracted from infected chick embryo cells was fractionated on sucrose gradients. Three types of viral RNA were synthesized by both viruses: the infectious 45 s RNA, 27 s “interjacent” RNA and a 20 s ribonuclease resistant double-stranded RNA.Ets-4 produced greater amounts of each RNA species than did encephalitis virus. Production of the 45 s infectious RNA by Ets-4 as measured by plaque assay was less than that of the parent virus, but the incorporation of radioactive uridine into this RNA species was greater, suggesting that the 45 s RNA was biologically defective. On a specific infectivity basis (infectious 45 s RNA/radioactive 45 s RNA) the 45 s RNA of Eta-4 possessed only 2% of the infectivity observed for its parent. Viral protein synthesis, measured by the complement fixation and hemagglutinin tests, induced by Ets-4 was depressed below that of the parent virus indicating that the increased RNA synthesis of the mutant did not result in correspondingly increased amounts of virus protein. The apparent defect in viral protein synthesis may be the result of a defect in viral RNA made by Eta-4.On the basis of the information available, it appeared that viral RNA synthesis in Eta-4 infected cells was out of control. Control seemed to be restored to the level and pattern of the parent by superinfection with the parent encephalitis virus or Venezuelan equine encephalitis virus but not with other viruses.