Figure 5.

Fluorescence-based H⁺ conductivity assay. The fluorescence of bacteria that harbor pHluorin, a pH-sensitive green fluorescence protein (GFP) [44], was examined as a function of the expressed viral chimera [46,47]. Protein levels were governed by the level of the inducer (50 μM IPTG), as indicated. At time 0, a concentrated acid solution was injected into the media. Consequently, a drop of the fluorescence ratio between excitation at 390 nm relative to excitation at 466 nm (shown on the left axis) is indicative of a pH decrease, as shown on the right axis. The ΔpH values indicated in the parentheses correspond to the difference in the pH after 30 s in bacteria that had undergone protein induction. Generic TM indicates a chimera in which MBP is fused at its carboxy terminus to the transmembrane domain of glycophorin A containing two monomerizing mutations [48,49]. + Rim is a sample in which rimantadine, a specific blocker of the influenza M2 channel [10], was added at a concentration of 50 μM. Note that rimantadine did not affect other proteins (data not shown). The results are an average of three independent experiments, with standard deviations depicted as error bars.