Analysis of the transcript encoding the latent Epstein-Barr virus nuclear antigen I: a potentially polycistronic message generated by long-range splicing of several exons.

The Epstein-Barr virus nuclear antigen (EBNA I) present in latently infected cells is encoded in a 2-kilobase exon contained in the BamHI K viral genomic fragment. This exon is, however, found within a 3.7-kilobase mRNA transcript. The origin of the remaining 1.7 kilobases is unknown, although it is not derived from adjacent Epstein-Barr virus DNA sequences. A 1.1-kilobase cDNA clone generated by primer extension using an oligonucleotide complimentary to a sequence 245 base pairs 3' to the putative initiation codon for EBNA I in the BamHI K fragment has been isolated. This clone contains seven exons (from the BamHI W, Y, U, E, and K viral genomic fragments), which are spread over approximately 70 kilobases of the viral genome. However, this clone does not appear to contain the complete 5' end of the transcript. In addition to the open reading frame in the exon encoding EBNA I, three other open reading frames are found in this transcript that potentially encode other viral antigens present in latently infected cells.