EBV BAC mutagenesis in E. coli. Recombination with linearized targeting vectors. This method allows deletions or exchanges of genetic material from the EBV DNA against foreign sequences. The latter can be mutated versions of an EBV gene, or DNA fragments of cellular or bacterial origin. Selection of successfully recombined BACs requires the introduction of an antibiotic resistance cassette flanked by Flp-recombinase target (FRT) sites. Transient introduction of the FLP recombinase allows excision of the antibiotic resistance cassette.