EPSTEIN-BARR-VIRUS LATENT MESSAGES WITH SHUFFLED LEADER EXONS - REMNANTS OF CIRCUMGENOMIC TRANSCRIPTION

The EBNA transcription unit which is active in Epstein-Barr virus-immo rtalized latently infected B lymphocytes covers approximately 60% of t he 172-kb genome, Since the genome exists as a circular double-strande d DNA molecule in latently infected cells, it is conceivable that comp lete copies are made during transcription, Rather than attempt to dete ct gigantic RNA molecules directly, we used RNA-PCR to detect incorpor ation of leader exons into mRNA in a shuffled order, The downstream U leader exon was detected spliced upstream of the internal repeat leade r exons W1 and W2 in the polyadenylated RNA fraction of spontaneous ly mphoblastoid cell lines, restricted phenotype BL cell lines Wanyanyi a nd Wewak2, and in B95-8, Raji, and Akata cells, Quantitative competiti ve RNA-PCR showed that the ratio of U exon-containing EBNA1 messages t o U exon-shuffled leader messages was approximately 10:1, with large v ariation from cell line to cell line, and was not affected by inductio n of the lytic cycle in B95-8, Raji, or Akata cells, Messages with shu ffled exons contained only the C2W1 alternative splice, which does not produce an initiator AUG methionine codon for EBNA4 gene expression, The results provide evidence for long-range exon skipping and imply th at genome-length transcripts may occur and participate in viral gene e xpression in latency,