FIG. 6.

Liposome binding is not blocked by HR2 peptides. Sucrose step gradients were used to separate liposomes by their buoyant densities. Soluble, oligomeric ASLV-A envelope (A) or ASLV-A virions (B) were incubated with or without soluble receptor (sTva) to activate envelope in the presence or absence of HR2 peptides. The R102 peptide was used at a concentration of 50 μg/ml (A), and R99 was used at 30 μg/ml (B). Each fraction (top, middle, bottom) was examined by SDS-PAGE and Western blotting with antisera against either the SU (A) or TM (B) subunit. Samples were loaded in the dense bottom fraction, so that liposome-associated material would float to the upper, less-dense fractions. The retarded migration of SU in the bottom fraction of the first gradient in panel A is an SDS-PAGE artifact.