Latent and viral replicative transcription in vivo from the BamHI K fragment of Epstein-Barr virus DNA.

We mapped one latent and two replicative messages transcribed in vivo from the BamHI K fragment of the Epstein-Barr virus genome. The exon encoding Epstein-Barr nuclear antigen (EBNA), a major latent product, is 2,028 bases; the 3' end of this exon occurs 30 bases after the polyadenylation signal AATAAA, and the 5' end occurs within a splice acceptor site. The open reading frame which encodes the EBNA peptide is completely contained within this coding exon. The exon was faithfully transcribed after transfection of cloned BamHI-K into either COS-1 or TK- mouse L cells. In lymphocytes the abundance of the EBNA message is increased after cycloheximide treatment. The two viral replicative genes completely contained in BamHI-K were not transcribed in line X50-7, in which the genome is tightly latent. In contrast to the EBNA message, these mRNAs of 1.3 and 2.1 kilobases are inducible with phorbol ester and are unspliced. Their promoter regions are similar to those of each other and to replicative promoters mapped in other regions of the Epstein-Barr virus genome (P. J. Farrell, A. Bankier, C. Seguin, P. Deininger, and B. G. Barrell, EMBO J. 2:1331-1338, 1983). An unusual feature of these replicative genes is that the smaller mRNA begins within a long open reading frame of the larger mRNA. The identification of the structure of latent and replicative genes within one DNA fragment will facilitate analysis of regulation of expression for the two life cycles of the virus.