Figure 4.

The pH dependence of formation of the GL23 and HA4-23 intermediates and their stability with time. (A) The GL23 and HA4-23 intermediates were generated and their ability to convert to fusion was measured after a 10-min (striped bars) or 40-min (open bars) incubation at 23°C at neutral pH. Fusion from HA4-23 (first and second columns) or GL23 (third and fourth columns) was induced either by increasing temperature to 37°C (first and third columns) or by treating with 0.5 mM CPZ (second and fourth columns). (B) The GL23 and HA4-23 intermediates were generated by decreasing pH to 5.0 (rather than to 4.8), with all other aspects of the protocol performed as usual. The extent of fusion induced by increasing the temperature to 37°C or by adding CPZ after maintaining the intermediates for 10 min was less than when pH had been decreased to pH 4.8.