FIG. 2.

ΔBMRF1 cells produce neither the BMRF1 protein nor lytic cycle late proteins. 293/ΔBMRF1 and 293/wt-EBV cells were transfected with an expression plasmid for the BZLF1 gene to induce the lytic cycle and stained with antibodies directed against the BMRF1 protein (the EA-D early antigen). Lytically induced 293/ΔBMRF1 cells do not produce the antigen, whereas mutant cells complemented with BMRF1 and wild-type cells do, confirming that the ΔBMRF1 genome lacks the BMRF1 gene. When the same cells were stained with antibodies directed against the gp350 or gp110 late antigen, 293/ΔBMRF1 cells were found to produce neither gp110 nor gp350. In contrast both complemented 293/ΔBMRF1 cells and wild-type cells stained positive for these antigens.