FIG. 7.

Determination of the pH required for optimal fusion induced by BDV G and kinetics of fusion. (A) Noninfected Ol cells and Ol cells persistently infected with BDV were treated with buffer at the indicated different pHs for 5 min, and at 45 min posttreatment, cells were fixed and nuclei stained with DAPI (4′,6-diamidino-2-phenylindole). (B) Numbers of syncytia induced at different pHs were determined by light microscopy. (C) Ol cells infected with BDV (MOI = 0.1) at 4°C were transferred to 37°C, and at the indicated times, NH₄Cl (20 mM) was added to inhibit endosomal acidification. At 48 h p.i., cells were fixed and subjected to IFA using a rabbit polyclonal serum to BDV N to identify virus-infected cells.