The Sendai virus membrane fusion mechanism studied using image correlation spectroscopy

The mechanism of Sendai virus membrane fusion to cultured cell membranes was studied. Viral lipids were labeled with the lipophilic dye, 4-(4-(dihexadecylamino)styryl-N-methylquinolinium iodine) (DiQ), and viral proteins were labeled using fluorescein isothiocyanate (FITC). The redistribution of these probes from the virus to cultured cells was followed using the technique of image correlation spectroscopy. This technique assayed the intensity change and the redistribution of these probes as fusion progressed from a more to less aggregated state. The lipid probe DiQ dispersed into the membrane of the target membrane at both 22 and 37 degrees C, while the FITC-labeled proteins dispersed only at 37 degrees C. Simultaneous labeling of virus with both of these probes showed that at 37 degrees C their redistribution proceeded at different rates. These data were consistent with the formation of a hemifusion intermediate during the fusion process.