FIG. 3.

NA protein levels in transfectant viruses. Wild-type (WT) influenza A/WSN/33 virus and transfectant D1, D2, and D3 (A) or D1/2 (B) virus were grown in MDBK cells and purified through 30 to 60% sucrose gradients. Proteins of purified viruses, untreated (−) or treated with PNGase F (+), were separated by SDS-PAGE (12% gel) and stained with Coomassie brilliant blue. Positions of untreated proteins are shown on the left; positions of proteins treated with PNGase F are indicated on the right. The position of PNGase F is shown on the right. Arrowheads indicate positions of the NA treated with PNGase F (17).