Figure 2.

Retrovirus vector titers on polyclonal NIH 3T3 cells transfected with the RDR expression vector pL(RDR)SN or the empty expression vector pLXSN. Both SNV and BaEV pseudotypes represent replication-competent virus, whereas RD114, GALV, and VSV-G were helper-free. The titer of replication-competent viral stocks used in these experiments was 4.1 × 10⁴ AP⁺ ffu/ml for SNV and 3.2 × 10⁴ lacZ⁺ ffu/ml for BaEV when assayed on D17 cells. The titer of LAPSN(GALV) was 5.3 × 10⁵ AP⁺ ffu/ml assayed on human cells. Each bar represents the mean ± SD of triplicate measurements, except for VSV-G, which represents the mean of duplicates. A representative experiment is shown; each determination was performed at least twice.