ISAV-M1 membrane association by liposome flotation. M1 protein was incubated overnight with liposomes under different conditions and floated on an Accudenz discontinuous gradient. Top (T), Middle (M), and Bottom (B) fractions of the discontinuous gradient were analyzed by SDS/PAGE and stained with Coomassie blue. Flotation assays of M1 with (A) PC:PS (50:50) 100 nm or 400 nm liposomes, and 100 nm PC:PS (75:25) liposomes; (B) 400 nm PC:PS (50:50) liposomes incubated with M1 the Tris buffer with 200 mM or 500 mM NaCl; (C) DMAB-treated M1 floated with 100 nm PC:PS (50:50) liposomes; (D) M1 N-terminal truncation (1–119) and C-terminal truncation (120–196) floated with 400 nm PC:PS (50:50) liposomes; (E) M1-3KA (K63, 66, 68A) and (F) M1-4KA (K30, 31, 32, 33A) at different concentrations floated with 400 nm PC:PS (50:50).