TABLE 2.

Quantitation of virus release^a

Virus	Approx. no. of cells infected (108)	Total U of NP harvested	U of NP harvested/106 cells	Fold decrease in U/cell relative to that for wt
rSV5	2.4	4,254	17.7	1.0
rSV5 HNΔ2-9	6.4	1,564	2.4	7.3
rSV5 HNΔ2-13	6.4	971	1.5	11.7

^awt rSV5, rSV5 HNΔ2-9, and rSV5 HNΔ2-13 were grown in MDBK cells, and at 7 days p.i. the culture media were harvested and virions were purified by centrifugation through two sequential sucrose gradients. Thirty-six equal fractions were taken from the top of each gradient, and fractions 13 to 36 were assayed for NP protein by quantitative dot blotting. The total amount of NP protein harvested (arbitrary units [U]) was calculated by summing the amounts of NP protein detected in the gradient fractions.