FIG 2.

R-K and E-K pairs at the 205-72 pair in HA decrease viral infectivity. (A and B) The HA pseudovirus infectivities of wild-type (WT), NCD, Bris, and Mex HAs containing R-H, H-H, H-K, R-K, and E-K pairs at the 205-72 pair (A) and of chimeric Mex-NCD and Mex-Bris containing the R-H, H-H, H-K, R-K, and E-K pairs at the 205-72 pair (B) are compared. Data are shown as the mean and standard deviation from three independent experiments. *, t test, P < 0.05. (Bottom) The levels of mature HA (HA2) in pseudoviruses shown by Western blotting were detected with rabbit antisera against the HA2 C helix. (C) Influenza viruses with Bris HA generated by reverse genetics (rg) and recovered from the supernatants of transfected cells (left) or after a single passage on MDCK cells (right). Infectivity was scored by quantifying the HAU on turkey red blood cells. The relative levels of HA in viruses recovered from the supernatants shown by Western blotting were detected with rabbit antisera against the HA2 C helix. The data shown are representative of those from two independent experiments.