Southern blot analysis of recombinants.

<p>BSC-40 cells were infected (or co-infected) with the different indicated viruses, and Southern blotted to detect recombinants. (A) The scheme used to collect samples for Southern blotting. Some DNA was extracted directly from virus-infected cells 24 h after infection. Alternatively, the viruses were plated, red fluorescent plaques subjected to two rounds of plaque purification, and the virus expanded to produce sufficient DNA for Southern blots. (B) Southern blot analysis of virus DNAs. DNA was extracted from virus-infected BSC-40 cells, as in panel (A), digested with <i>Xho</i>I endonuclease, and blotted using biotin-labeled pE/L and cro probes (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005824#ppat.1005824.g007" target="_blank">Fig 7A</a>). A novel 0.8 kbp DNA fragment is diagnostic for recombinants (and is also found in the pE/L-mCherry-cro control virus), but this 0.8 kbp fragment is only detected after the recombinant viruses are subjected to several additional rounds of plaque purification.