RESCUE OF THE EPSTEIN-BARR-VIRUS BZLF1 MUTANT, Z(S186A), EARLY GENE ACTIVATION DEFECT BY THE BRLF1 GENE-PRODUCT

Expression of the Epstein-Barr virus (EBV) immediate-early protein, BZ LF1 (Z), is sufficient to disrupt viral latency. Z transcriptionally a ctivates the EBV early genes by binding to upstream Z-responsive eleme nts (ZREs). Recently, a serine-to-alanine mutation of Z residue 186 (w ithin the basic DNA binding domain) was shown to inhibit the ability o f Z to induce lytic infection in latently infected cells, although the Z(S186A) mutant could still bind several known ZREs and activated an early EBV promoter (BMRF1) in transient reporter gene assays (Francis, A. L., Gradoville, L., and Miller, G. (1997). J. Virol. 71, 3054-3061 ). We now show that a specific deficiency in the ability to bind to ZR E elements in the immediate-early BRLF1 promoter may account for the i nability of Z(S186A) to activate BRLF1 expression. Furthermore, we dem onstrate that the ability of Z(S186A) to induce early BMRF1 and BH RFI gene expression is rescued by cotransfection with a BRLF1 expression vector. However, the Z(S186A)/BRLF1 (R) combination cannot induce full lytic replication, suggesting that Z(S186A) may also be deficient in a replication-specific function. These results suggest that in the con text of the intact viral genome, both Z and R expression are required for activation of early gene transcription in latently infected cells, (C) 1998 Academic Press.