ALV was thought to fall into the latter category, but researchers have shown that it fuses as a result of both receptor binding and low pH, probably in the endosome. He placed ALV and target cells in a buffer that prevents the acidification of the endosome. In the 1990 classic experiments, researchers had shown that inhibiting acidification of the endosome failed to affect ALV's ability to fuse, hence its classification as pH-independent. Mothes expected the same. Mothes and his colleagues decided to rerun the other classic experiments to see if their results were just a fluke.
Cells infected by virus often fuse together, producing multinucleated cells, or syncytia.
We looked for 10 and saw syncytia. Timing, they realized, could provide an answer. Earlier researchers, following standard practice, waited days before monitoring the effects of the acid-inhibiting reagents on fusion. Because the reagents were toxic and had to be washed out after six hours, the researchers could detect only those viruses that remained inhibited after the six-hour treatment. Using their PCR assay, Mothes and his colleagues were able to monitor the fusion process much earlier, before the acid-inhibitor was washed out.