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. 2003 Mar;77(6):3851–3858. doi: 10.1128/JVI.77.6.3851-3858.2003

FIG. 2.

FIG. 2.

Contamination of recombinant virus stocks by RCVs. Standard and chimeric recombinant virus stocks were produced by cotransfecting 293T cells with vector DNA and the corresponding helper plasmid (described in the legend of Fig. 1), while pseudotype virus stocks were produced by cotransfection of standard pMVMp/GFP and phH1/GFP with H1 helper and MVMp helper DNA, respectively, resulting in MVMp/GFP(H1) and hH1/EGFP(MVM). Virus stocks were harvested 72 h posttransfection and purified by centrifugation on iodixanol gradients, and virus titers were determined on NB324K cells by a hybridization assay using a specific 32P-labeled NS DNA probe consisting of a 703-bp EcoRV-EcoRI restriction fragment of either pMVMΔ800 or phH1Δ800. Total levels of virus production are expressed as RU per 2 × 106 transfected cells (grey bars). The proportion of replication-competent viruses present in the recombinant virus stocks was determined by plaque assay and expressed as PFU per 2 × 106 transfected cells (black bars). The results shown are the averages of at least three independent experiments, with standard deviations indicated by the error bars.