Table 7 
Double Infections with SFV Variants* 
SFV-hTR/Helper 
2 
LacZ Positive Cells 
SFV-LacZ/Helper 1 Virus Added 
Virus Added 
(IU) 
(MOI) 
1 
1000 
0 
2 
1000 
3 
1 
1400 
5 
2 
800 
10 
0 
800 
15 
0 
1000 
20 
1 
100 
30 
1 
600 
*2.1 x 10 5 BHK cells were infected with activated SFV-hTR/Helper 2 virus at various 
MOI (titre determined by IF). In each experiment, lacZ-helper 1 virus was added at 
either 
1 IU or 1000 IU, and cells were incubated overnight. Cells were then stained with Xgal 
for expression of LacZ. 
In the next set of experiments (Table 8), 10 7 -10® BHK cells were infected with 
SFV3-lacZ/Helper 2 virus, using a wider range of MOI. In parallel, wild type 
SFV (1, 3, or 5 IU) was added to assess interference. Altogether, ten independent 
recombinant Helper 2-derived stocks, totalling 2xl0 10 activated particles, were 
tested for the presence of replication-competent virus, by infecting a population 
of about 10 9 cells -- with no evidence of wild type virus. 
The reconstitution experiments indicated that as few as one wild type SFV was 
detectable at an MOI of 17, and five wild type SFV at an MOI of 34, comprising 
a total of 3 x 10 9 SFV-lacZ/Helper 2 particles tested. 
Recombinant DNA Research, Volume 18 
[455] 
