Fig. 3.

Fluorescence dequenching test.

FluV envelope proteins are labeled with rhodamine chloride (R-18). When the density of fluorescent protein molecule is too compact, the fluorescence is quenched and cannot be detected. After endocytosis of the virion, when fusion of viral envelope to cell membrane is completed, fluorescent molecules move to cell membrane, are dispersed in the membrane, and the self quenched fluorescence is recovered. The degree of the fluorescence dequenching (FDQ) is measured by a fluorometer.