Figure 5.

Sensitivity of the intermediates to proteolytic digestion by proteinase K. GL23 or HA4-23 was generated, followed by an additional 10-min incubation at 23°C in the absence (−) or presence (+) of proteinase K (0.01 mg/ml for G520L and 0.05 mg/ml for HA). The reaction was stopped by washing cells three times with PBS/raffinose, fusion was triggered by increasing temperature to 37°C (open bars) or by treating with 0.5 mM CPZ (striped bars), and transfer of CF was measured. Whereas for HA4-23 a proteinase treatment that abolished the ability of increased temperature to induce fusion also eliminated the ability of CPZ to promote fusion, for GL23 the CPZ sensitivity was retained.