Murine gammaherpesvirus 68 encodes tRNA-like sequences which are expressed during latency

Murine gammaherpesvirus 68 (MHV-68) is a virus of wild rodents and is a convenient small animal model for studies of gammaherpesvirus pathogenesis. We have sequenced 6162 bp at the left end of the MHV-68 genome and identified two unique open reading frames (ORFs) (ORF2 and ORF3) and an ORF (ORF1) which displays similarity to poxvirus members of the serpin family. Interspersed with the ORFs is a family of eight novel tRNA-like sequences sharing tRNA-like predicted secondary structures and RNA polymerase III promoter elements. These sequences are expressed to high levels during lytic infection and are processed into mature tRNAs with post-transcriptionally added 3' CCA termini, indicating their recognition as tRNAs by cellular machinery. Acidic Northern analysis of four tRNAs tested has demonstrated that they are not aminoacylated by aminoacyl-tRNA synthetases present in the infected cell. Thus, it is currently unclear what biological function these uncharged viral tRNA-like sequences may fulfil. In situ hybridization analysis has shown that in addition to being expressed within productively infected tissues during acute stages of infection, the tRNA-like sequences are abundantly expressed within splenic germinal centres of latently infected mice. Therefore, the MHV-68 viral tRNAs represent a marker for latent infection and constitute the first report of tRNA-like sequences encoded by a virus of eukaryotes.