Yeast killer toxin: site-directed mutations implicate the precursor protein as the immunity component.

Area of Science:

• Molecular biology
• Yeast genetics
• Protein processing

Background:

• Yeast killer toxin is a secreted protein conferring toxicity to sensitive yeast strains.
• Both the toxin and immunity are encoded by a single gene producing a precursor polypeptide.
• The precursor undergoes proteolytic processing to yield active toxin subunits.

Purpose of the Study:

• To identify the specific region of the yeast killer toxin precursor gene responsible for immunity.
• To understand the mechanism by which the precursor confers immunity.

Main Methods:

• Site-directed mutagenesis was employed to alter specific regions of the precursor gene.
• Analysis of mutant strains to assess toxin secretion, precursor processing, and immunity phenotype.

Main Results:

• A specific region, spanning the C-terminal alpha subunit and N-terminal gamma peptide, was identified as essential for immunity.
• Mutations outside this region allowed immunity but impaired precursor processing.
• The precursor itself can confer immunity, independent of full processing.

Conclusions:

• The identified region of the precursor is critical for conferring immunity to yeast killer toxin.
• The precursor may confer immunity by competing with mature toxin for a membrane receptor binding site.