PCR analysis of the D4R deletion in the defective virus dMVA-ZG. Genomic DNA of dMVA-ZG was subjected to PCR amplification using a primer pair that frames the D4R deletion (Lane 5). Negative controls were run without any template (Lane 2), with uninfected cDF-1 (Lane 3) cells and with the recombination plasmid pDM-Zgpt (Lane 4). Spike controls were performed with dMVA-ZG containing MVA-wt at 0.001-1% (Lanes 6-9). 1% corresponds to 1 000 pfu virus. A reaction with MVA-wt alone is shown on lane 10.