A genetic analysis of resistance to nystatin inSaccharomyces cerevisiae

Abstract

1. A number of stable nystatin-resistant mutants of the yeast Saccharomyces cerevisiae have been isolated from platings of a sensitive wild-type strain on low concentrations of the antibiotic.2. These mutants were found to be resistant to 10, 15 or 60 units of drug/ml.3. Analysis of meiotic segregants from crosses of these mutants to wild-type indicate that resistance is determined by two types of genes; resistance genes and modifiers.4. Functional analysis of the mutants demonstrated the existence of three recessive resistance genes, nys-l, nys-2 and nys-3 and that nys-1 and nys-2 were linked.5. Genetic analysis showed that nys-1 was affected by two modifiers, Mnys-1 and Mnys-2, but that only Mnys-2 affected nys-2 and nys-3.6. The modifiers Mnys-1 and Mnys-2 are dominant.7. An investigation of the effects of temperature and medium on resistance demonstrated marked interactions between genotype and environment for both the resistance genes and the modifiers.8. Second-step mutants have been isolated by plating first-step mutants on higher concentrations of the drug. Some of these are resistant to 800 units/ml.9. Some possible mechanisms of nystatin resistance are discussed.