FIG. 4.

Lymphoblastoid cell line (LCL) generated by infection of primary B cells with ΔBMRF1 virus contains the mutant genome only. Genomic DNA extracted from LCL generated by infection of B cells with either wt EBV or complemented ΔBMRF1 virus (ΔBMRF1-LCL) was cleaved with the BamHI restriction enzyme and subjected to agarose gel electrophoresis, and Southern blotting analysis was performed with a probe for the BMRF2 gene. Blots were hybridized with a BMRF2-specific probe. The BMRF2 gene is located on the BamHI-M fragment of the EBV genome and allows distinction between the wild-type BamHI-M fragment, which is 4.7 kb in size, and the BamHI-M fragment of the ΔBMRF1 mutant, which is 5.0 kb (Fig. 1). This analysis confirms that B cells immortalized with the ΔBMRF1 virus carry the mutant gene while B cells infected with wt EBV carry an intact BamHI-M fragment.