FIG. 5.

Inhibition of cell-cell fusion by HR2 peptide occurs prior to acid activation. Transfected 293T cells expressing ASLV-A envelope and HIV-1 Tat were seeded in an equimolar ratio with HeLa-MAGI cells stably expressing the Tva receptor. Cells were allowed to attach for 3 h, washed, pulsed with low-pH medium (pH 5.25), washed again, and assayed for β-galactosidase activity 12 h later. R99 was included at 5 μg/ml during the 3-h attachment period (lane 3), during the acid pulse (lane 4), during the 12-h recovery phase (lane 5), or throughout the entire assay (lane 2). Lane 1 is a control in which R99 was not used.