Infectious Japanese encephalitis virus RNA can be synthesized from in vitro-ligated cDNA templates

Japanese encephalitis virus (JEV) is a positive-stranded enveloped RNA virus that belongs to the family Flaviviridae. Genomic JEV RNA is approximately 11 kb long and encodes 10 proteins, 3 structural and 7 nonstructural. A full-length cDNA copy of the JEV genome was constructed by in vitro ligation of two cDNA fragments which encode the 5′ (nucleotide positions 1 to 5576) and 3′ (nucleotide positions 5577 to 10976) halves of the genome. T7 RNA polymerase transcripts of the ligated full-length cDNA template were infectious when transfected into BHK-21 cells. To identify the recombinant virus, a silent mutations was introduced into the clone encoding the 3′ half of the genome, which abolished an XbaI site at nucleotide position 9131. Virus recovered by transfection with the transcripts contained this silent mutation, confirming its identity. Recombinant and parent viruses were identical with respect to growth and plaque production in BHK-21 cells, envelope protein expression in C6/36 cells, and neurovirulence and immunogenicity in mice. Repeated attempts to obtain infectious RNA by transcription from full-length JEV genome cDNA templates cloned into plasmid vectors were unsuccessful. Synthesis or infectious JEV RNA from in vitro-ligated JEV cDNA templates will be useful for molecular and genetic studies of flavivirus replication and virulence.