FIG. 3.

Virus-containing supernatant harvested from NIH 3T3 (A), HEK293 (B), and U87-MG (C) cells in infection cycle 1 was used to infect fresh cells of the corresponding cell line, and 50 μM zidovudine was applied 24 h postinfection to prevent secondary infection events. The relative quantity of integrated proviral copies per infected producer cell and the relative quantity of nascent virus released into the supernatant from each infected producer cell were determined by real-time PCR and real-time RT-PCR, respectively. Values shown indicate the numbers of nascent virions released per proviral copy in infected producer cells (black bars), the quantity of eGFP-positive cells generated per virus particle (gray bars), and the cumulative effect of the differences in nascent virus particle production and infectivity (white bars), in each case relative to the value obtained for ACE-GFP. Statistical significance of differences between vectors is indicated by asterisks (t test; P < 0.0001 is indicated by three asterisks, P < 0.001 is indicated by two asterisks, and P < 0.02 is indicated by one asterisk).