Kex2‐dependent processing of yeast K1 killer preprotoxin includes cleavage at ProArg‐44

Abstract

The K₁ killer toxin of Saccharomyces cerevisiae consists of 103‐ and 83‐residue α and β components whose derivation, from a 316‐residue precursor preprotoxin, requires processing at the αN‐terminus (after ProArg‐44), the αC‐terminus (after ArgArg‐149) and at the βN‐terminus (after LysArg–233). These processing events occur after translocation to the Golgi and have been investigated using β‐lactamase fusions. Signal peptidase cleavage of the precursor, predicted to occur after Ala‐26, was confirmed by N‐terminal sequence analysis of Ala‐34 and IIe‐52 fusions. Cleavage at all of the other predicted processing sites, including ProArg‐44, is dependent on activity of the Kex2 protease. A fourth Kex2‐dependent cleavage occurs at LysArg‐188. Implications for the specificity of Kex2 cleavage and preprotoxin processing are discussed.