Immunity to killer toxin K1 is connected with the golgi-to-vacuole protein degradation pathway

Abstract

Killer strains of Saccharomyces 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 of S. cerevisiae strains with deletions in various genes transformed by the pYX213+M1 vector carrying cDNA coding for the K1 toxin under the control of the GAL1 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 genes VPS1, VPS23, VPS51 and VAC8 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.

Expression of K1 Toxin Derivatives in Saccharomyces cerevisiae Mimics Treatment with Exogenous Toxin and Provides a Useful Tool for Elucidating K1 Mechanisms of Action and Immunity

“…This observation is in agreement with published data describing an incomplete mediation of immunity by the toxin precursor itself after expression from an episomal plasmid [ 14 ]. Likewise, the intracellular expression of the K1-tox derivative caused some PI-positive cells (15.3%, Figure 2 D).…”

Yeast Viral Killer Toxin K1 Induces Specific Host Cell Adaptions via Intrinsic Selection Pressure

“…The reduced pore formation in strain KIM01s can probably be explained by the strongly decreased secretion of the toxin, whereas the molecular machinery conferring immunity in the superkiller T158c is likely to be optimally adjusted to reinternalized toxin molecules. This leaky immunity correlates with findings displaying the same phenotype when K1 toxin is expressed via a centromeric plasmid (19). However, we previously were able to demonstrate that the formation of toxin-induced pores takes place considerably before a significant decrease in cell viability of sensitive cells can be observed (16).…”

Messenger RNAs transcribed from yeast linear cytoplasmic plasmids possess unconventional 5’ and 3’ UTRs and suggest a novel mechanism of translation

“…The most likely reason is that K1 killer toxin is more active at 24°C than at 37°C, even though we cloned the coding sequence of the K1 super-killer variant that shows enhanced thermal stability (107). We previously showed that K1 preprotoxin produced artificially from the nuclear plasmid does not fully support the immunity phenotype of the host cells (106). Higher K1 toxin stability at 24°C thus probably led to the slightly slower growth.…”

“…We prepared the M1 cDNA, cloned a gene coding for the prepro-K1 killer toxin into a yeast shuttle expression plasmid (106) under the control of the strong constitutive TPI promoter (plasmid pYX212::M1) and introduced this expression plasmid into the S. cerevisiae CWO4 ρ 0 strains carrying all three CDC33 alleles described above. The resulting strains display K1 killer and immunity phenotypes at the permissive temperature (24°C) (Fig.…”