A molecular target for viral killer toxin: TOK1 potassium channels

Killer strains of S. cerevisiae harbor double-stranded RNA viruses and secr ete protein toxins that kill virus-free cells. The K1 killer toxin acts on sensitive yeast cells to perturb potassium homeostasis and cause cell death . Here, the toxin is shown to activate the plasma membrane potassium channe l of S. cerevisiae, TOK1. Genetic deletion of TOK1 confers toxin resistance ; overexpression increases susceptibility. Cells expressing TOK1 exhibit to xin-induced potassium flux; those without the gene do not. K1 toxin acts in the absence of other viral or yeast products: toxin synthesized from a cDN A increases open probability of single TOK1 channels (via reversible destab ilization of closed states) whether channels are studied in yeast cells or X. laevis oocytes.