Mak mutants of yeast: mapping and characterization

Area of Science:

• Molecular biology
• Yeast genetics
• Virology

Background:

• Killer strains of Saccharomyces cerevisiae harbor M double-stranded (ds) RNA within virus-like particles, enabling toxin secretion.
• Most yeast strains also possess L dsRNA, a larger dsRNA molecule.
• Understanding the genetic basis for dsRNA maintenance is crucial for yeast biology.

Purpose of the Study:

• To identify and map chromosomal genes (mak genes) essential for maintaining the M dsRNA in killer yeast.
• To investigate the effects of mutations in these mak genes on dsRNA stability and yeast physiology.

Main Methods:

• Genetic mapping of mutations in eight chromosomal mak genes.
• Analysis of dsRNA content (M and L) in wild-type and mutant yeast strains.
• Phenotypic characterization of mak mutants, including growth rates and temperature sensitivity.

Main Results:

• Eight chromosomal mak genes were mapped across the yeast genome, showing no complex formation.
• Mutations in these mak genes led to the loss of M dsRNA but not L dsRNA.
• Specific mutations (e.g., mak3-1) affected L dsRNA levels, while others (e.g., mak16) caused temperature-sensitive growth, and several resulted in slow growth.

Conclusions:

• The identified mak genes are specifically required for the maintenance of M dsRNA in killer yeast.
• These genes are essential for yeast viability and growth, with distinct mutations conferring different physiological defects.
• The study provides a genetic framework for understanding M dsRNA maintenance and its impact on killer yeast phenotypes.