Immunity to killer toxin K1 is connected with the golgi-to-vacuole protein degradation pathway
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Killer strains ofSaccharomyces cerevisiae producing killer toxin K1 kill sensitive cells but are resistant to their own toxin. It is assumed that in the producer, an effective interaction between the external toxin and its plasma membrane receptor or the final effector is not possible on the grounds of a conformation change of the receptor or its absence in a membrane. Therefore, it is possible that some mutants with defects in intracellular protein transport and degradation can show a suicidal phenotype during K1 toxin production. We have examined these mutants in a collection ofS. cerevisiae strains with deletions in various genes transformed by the pYX213+M1 vector carrying cDNA coding for the K1 toxin under the control of theGAL1 promoter. Determination of the quantity of dead cells in colony population showed that (1) the toxin production from the vector did not support full immunity of producing cells, (2) the suicidal phenotype was not connected with a defect in endocytosis or autophagy, (3) deletants in genesVPS1, VPS23, VPS51 andVAC8 required for the protein degradation pathway between the Golgi body and the vacuole exhibited the highest mortality. These results suggest that interacting molecule(s) on the plasma membrane in the producer might be diverted from the secretion pathway to degradation in the vacuole.
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