FIG. 1.

Influenza virus-endosome fusion visualization method. (A) Structures of DiOC18 and R18, which can be incorporated into the virus membrane. ex., excitation; em., emission. (B) Schema outlining the fluorescence color shift induced by membrane fusion between a labeled virus and an endosome. (C) Fluorescence spectra of labeled virus (−SDS) and solubilized virus (+SDS). Extreme dilution of the probes increases green (510 nm) fluorescence and faintly alters red (586 nm) fluorescence. From the spectra, virus fusion could be detected by monitoring green and red fluorescence simultaneously using two detectors with a confocal microscope. The labeled viruses were colored red before fusion, as shown in panel B, by tuning the red channel detector, which has greater sensitivity than the green channel detector.