Yeast Killer Toxin: Purification and Characterisation of the Protein Toxin from Saccharomyces cerevisiae

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Abstract
Killer toxin from killer strains of S. cerevisiae was isolated from concentrates of extracellular medium by precipitation in poly(ethylene glycol) and chromatography through glyceryl-controlled-pore glass. The toxin migrated as a single protein band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A MW of 11470 was determined for the toxin protein from its electrophoretic mobility and amino acid composition. Gel filtration of the active toxin indicated that the 11470-MW monomer was the active unit. Electrophoretic comparison of extracellular concentrates from a killer strain and an isogenic non-killer showed the presence of the toxin protein only in the killer-derived material. The activity of the toxin was most stable between pH 4.2 and 4.6. At 30.degree. C toxin from a superkiller strain was more stable than that from a normal killer.