FIG. 3.

Cell-cell fusion assay of the alanine-scanning mutants. COS-1 cells were transfected with the pTMT expression vector encoding either the mutant or wild-type env genes. COS-1 cells expressing glycoproteins were mixed at a 1:2 ratio with HOS-CD4/LTR-hGFP cells and replated. The cells were analyzed for expression of GFP and quantitated by FACS 36 h later as described in Materials and Methods. The * indicates syncytium formation in the context of full-length glycoprotein. The mean percentage (± the standard deviation) of GFP-expressing cells relative to wild type from three independent experiments is shown for each of the mutants.