FIG. 2.

Growth curves of different mutant viruses. MDCK cell monolayers were infected with viruses at an MOI of 0.001 and maintained at 33°C in VGM without (A) or with (B) 0.5 μg of TPCK-treated trypsin/ml. At different time points p.i., aliquots of culture supernatant were collected and titrated for infectious viruses by PFU assay. ▴, WT; ⋄, NA3A2; □, NA2A5; Δ, NA3A7; ×, NA4A10; Ж, NA5A14; ○, NA4A19; ♦, NA4A23; •, NA5A27; +, NA5A31; −, NA(1T2N)TR; ▪, NATRNA. Results represent averages of the results from four independent experiments.