Assessing the EBV BAC structure by restriction enzyme analysis. (A) Schematic overview of the EBV genome indicating the position of the various DNA repeats. IR: internal repeats, TR: terminal repeats, FR: family of repeats. (B) Restriction analysis of EBV BACs stably transfected into 293 cells. The left panel shows the predicted position of viral fragments after BamHI restriction. The right panel shows actual examples of abnormal EBV BACs rescued from producer cell lines. One EBV BAC carried fewer NotI repeats than the control (lane 1, purple arrow), another EBV BAC contained fewer TRs but more FRs (lane 2 red and green arrows, respectively), and a third recombinant carried fewer BamHI-W repeats (lane 5, blue arrow). Examples of large deletions (lane 3 and 4) are also shown. All of these abnormal clones were discarded. wt: wild type.