Table 2 
Frequency of Replication-competent Virus in 
Stocks of Packaged SFV3-lacZ/Helper 1 
Titre of Stock 
Numbers IU Added Per Plate b 
IU/ml* 
10 4 
10 5 
10 6 
2 x 10 6 
0 
5 
ND 
1 x 10 7 
0 
3 
ND 
1.2 x 10 7 
0 
2 
ND 
3.6 x 10 7 
0 
2 
24 
5.3 x 10 7 
5 
66 
>200 
9 x 10 7 
5 
157 
>200 
9 x 10 7 
11 
181 
>200 
1.1 x 10 8 
12 
100 
>200 
1.5 x 10 8 
0 
2 
19 
2 x 10 8 
1 
26 
>200 
2.1 x 10 8 
2 
27 
>200 
2.5 x 10 8 
2 
23 
>200 
2.5 x 10 8 
0 
0 
1 
3 x 10 8 
0 
5 
49 
7 x 10 8 
0 
6 
57 
1 x 10 9 
0 
0 
7 
•Titer was determined by infecting BHK cells for 16 hours, and staining fixed cells with Xgal. 
b Plaque forming units per 10 4 , 10 5 , or 10 6 1.U. of packaged SFV3-LacZ/helper 1. 
ND, not determined 
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Recombinant DNA Research, Volume 18 
