FIG. 4.

Characterization of LWYIK motif mutant Env proteins. (A) Cell surface expression. HeLa cells mock transfected (control) or transfected with the WT or mutant proviruses were metabolically labeled with [³⁵S]methionine and surface biotinylated with sulfo-N-hydroxysuccinimide-biotin. Levels of Env proteins expressed in cells (top panel) or on the cell surface (bottom panel) were assessed as described in Materials and Methods. (B) CD4-binding ability. HeLa cells transfected with pSVE7puro(ΔKS) (control), WT, or mutant pSVE7puro plasmids in the presence of pIIIextat were metabolically labeled with [³⁵S]methionine. Levels of Env proteins expressed in cells (top panel) and the CD4-binding ability of Env proteins (bottom panel) were determined. (C) Oligomerization ability. HeLa cells were transfected with pSVE7puro(ΔKS) (control), WT, or TC mutant pSVE7puro plasmid or cotransfected with the TC plasmid along with the WT or LWYIK motif plasmids in the presence of pIIIextat. Levels of Env proteins expressed in cells (top panel) and the self-assembly abilities of the Env proteins (bottom panel) were determined.