Latency of Epstein-Barr virus is stabilized by antisense-mediated control of the viral immediate-early gene BZLF-1

The ability of the Epstein-Barr virus (EBV) to avoid lytic replication and to establish a latent infection in B-lymphocytes is fundamental for its lif elong persistence and the pathogenesis of various EBV-associated diseases. The viral immediate-early gene BZLF-1 plays a key role for the induction of lytic replication and its activity is strictly regulated on different leve ls of gene expression. Recently, it was demonstrated that BZLF-1 is also co ntrolled by a posttranscriptional mechanism. Transient synthesis of a mutat ed competitor RNA saturated this mechanism and caused both expression of th e BZLF-1 protein and the induction of lytic viral replication. Using short overlapping fragments of the competitor, it is shown that this control acts on the unspliced primary transcript. RT-PCR demonstrated unspliced BZLF-1 RNA in latently infected B-lymphocytes in the absence of BZLF-1 protein. Du e to the complementarity of the gene BZLF-1 and the latency-associated gene EBNA-1 on the opposite strand of the genome, we propose an antisense-media ted mechanism. RNase protection assays demonstrated transcripts in antisens e orientation to the BZLF-1 transcript during latency, which comprise a com parable constellation to other herpesviruses. A combined RNAse protection/R T-PCR assay detected the double-stranded hybrid RNA, consisting of the unsp liced BZLF-1 transcript and a noncoding intron of the EBNA-1 gene. Binding of BZLF-1 transcripts is suggested to be an important backup control mechan ism in addition to transcriptional regulation, stabilizing latency and prev enting inappropriate lytic viral replication in vivo. (C) 1999 Wiley-Liss, Inc.