Mapping the major transcripts of ground squirrel hepatitis virus: the presumptive template for reverse transcriptase is terminally redundant.

The ground squirrel hepatitis virus (GSHV) belongs to a recently defined class of viruses with open circular DNA genomes that encode proteins in extensively overlapping reading frames and appear to replicate via RNA intermediates. We have determined the primary structure of the major GSHV transcripts in the livers of infected ground squirrels. Both major classes of transcripts, 2.3 kb and 3.5 kb, are plus-stranded, unspliced, polyadenylated at a common position, and display heterogeneous 5' ends that can encode proteins with different amino termini. The 2.3 kb transcripts, like their structural analogs transcribed from human hepatitis B virus DNA, are likely mRNAs for products of the major surface antigen and presurface coding domains. The 3.5 kb transcripts are likely mRNAs for one or more products of the core antigen reading frame; these transcripts also encompass the entire genome and contain terminal redundancies of 130-160 nucleotides that include a putative initiation site for reverse transcription.