Fig. 6.

Oligomerization assay. BSR-T7 cells were infected at an MOI of 10 with viruses containing wild-type or altered G proteins. Cells were exposed to [³⁵S]Met-Cys for 20 min and after the chase period were centrifuged over a sucrose gradient and examined for their trimerization as described in Materials and Methods. Wild-type G was found in the heavier fractions (bottom) of the gradient for fractions at a pH of ≤6.2, where its conformational change takes place. Above pH 6.2, wild-type G was found in both monomeric and oligomeric fractions. W72A, Y73A, and Y116A look similar to the wild type except their transition occurs at pH 6.0. A117F/E76K and E76K show a transition at a more neutral pH, between 6.6 and 6.4, similar to their cell-cell fusion profile.