Fig. 8.

Protection of viral HN glycoprotein from proteinase K digestion. (A). Virus was attached to ELL-0 cells for 1 h at 4 °C. Entry was initiated by incubation at 37 °C for the indicated times. Cells were treated with proteinase K, lysed, and viral HN protein was detected by Western blotting with polyclonal anti-NDV antibodies. (B) Virus was attached to MEB4 (lanes 1, 2, 5, and 6) and HeLa (lanes 3, 4, 7, and 8) cells for 1 h at 4 °C. Samples were then incubated at 37 °C for 10 min (lanes 1, 3, 5, and 7) or held at 4 °C (lanes 2, 4, 6, and 8), treated with proteinase K for 1 h at 4 °C, and lysed as detailed in Materials and methods. NDV-HN protein was detected by Western blotting.