PROTECTION BY STEROLS AGAINST THE CYTOTOXICITY OF SYRINGOMYCIN IN THE YEAST SACCHAROMYCES-CEREVISIAE

A brief exposure (ca 20 min) of the yeast Saccharomyces cerevisiae to the phytotoxin syringomycin was sufficient to kill the cell. The protective effect of sterols against this cytotoxicity of syringomycin was investigated. Syringomycin was much more toxic to growing cells than to stationary-phase cells. The cytotoxicity of syringomycin was reduced in an environment containing sterols. Cytotoxicity of syringomycin at 3 mug ml-1 (ca 2.5 mum) was completely abolished by the simultaneous presence of 10 mum-cholesterol in the medium. Cholesterol acetate had no protective effect. Ergosterol, sitosterol and stigmasterol also protected against syringomycin, but they were less effective than cholesterol. The protective effect of sterols against the action of syringomycin is consistent with our hypothesis that membrane ergosterol is a critical component for syringomycin-binding as suggested by recent genetic studies.