pH-dependent accumulation of the vesicular stomatitis virus glycoprotein at the ends of intact virions.

The electron microscope was employed to examine the effect of pH on the distribution of the vesicular stomatitis virus glycoprotein (VSV G-protein) on the surface of intact virions. Both rotary shadowed and negatively stained preparations demonstrated that whereas at neutral pH the glycoprotein was evenly distributed along the virus membrane, at pH 5.5 it was concentrated at the ends giving the overall virion a distinct bilobed or bipolar morphology. Negatively stained specimens showed that the shape of individual glycoprotein spikes was not greatly different at pH 5.5 compared to pH 7.5. The most dramatic effect was in their distribution along the virus membrane. The uniform glycoprotein distribution observed at neutral pH changed rapidly (t1/2 less than 1 min at 21 degrees) to the bipolar state when the pH of the medium was shifted from pH 7.5 to pH 5.5, and it reappeared somewhat more slowly (t1/2 = 2 min at 21 degrees) when the virus was returned to pH 7.5. Our observations support the view that the VSV glycoprotein is able to move laterally in the plane of the virion membrane to produce the terminal G-protein clusters found at low pH. They further suggest that the virion ends may be preferred as sites for the low pH-dependent membrane fusion process involved in initiation of infection by VSV.