A glycosylated protoxin in killer yeast: models for its structure and maturation.
The type 1 killer phenotype in S. cerevisiae, mediated by secretion of an 11.5 kilodalton (kd) protein toxin, is cytoplasmically determined by the 1.9 kb M1-dsRNA plasmid. Maintenance of M1-dsRNA is dependent on the 4.5 kb L1-dsRNA because L1 encodes the capsid protein of the virus-like particles that separately encapsidate both dsRNA species. We have shown that in vitro translation of denatured M1-dsRNA produces M1-P1, a 32 kd protein containing the toxin peptides. We now demonstrate the presence of an unstable, 42 kd, membrane-associated, glycosylated protoxin in killer cells, probably derived from M1-P1 by cotranslational processing, and glycosylation. In vitro cotranslational processing of M1-P1, derived both from in vivo mRNAs and from denatured M1-dsRNA, produces a product resembling protoxin. Processing involves loss of 1.6 kd of protein, presumably an N-terminal leader peptide, and glycosylation. This information, together with data on in vitro expression of suppressive deletion mutants of M1-dsRNA, allows construction of testable models for the functional sequence of M1-P1 and for its maturation to toxin.
D002462:Cell Membrane / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D008970:Molecular Weight; D009183:Mycotoxins / Q000235:genetics*; D010957:Plasmids; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D012330:RNA, Double-Stranded / Q000235:genetics; D012331:RNA, Fungal / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000502:physiology*
D006023:Glycoproteins; D008565:Membrane Proteins; D009183:Mycotoxins; D012330:RNA, Double-Stranded; D012331:RNA, Fungal; D012333:RNA, Messenger