Effect of the petite mutation on maltose and alpha-methylgucoside fermentation inSaccharomyces cerevisiae

Mitochondrial integrity and maltose utilization in yeast

Strains of the yeast Saccharomyces cerevisiae able to utilize maltose only in the presence of functional mitochondria have been described. Two such strains Z104-4B and Z109-1C were isolated as revertants from parental strains unable to utilize maltose. These strains are unique in the sense that although they produce inducible maltase for normal growth on maltose agar plates in the presence of functional mitochondria, they are very poor fermenters of maltose under anaerobic condition. Glycerol negative mutants isolated from these strains simultaneously lose the ability to utilize maltose. One of the manganese induced glycerol negative mit- mutants Z104-4B-Mn1, reverts concomitantly to growth on glycerol and maltose agar plates. On the basis of results presented in this paper, we propose the possibility of existence of two alternate mechanisms for maltose utilization in yeast. An oxidative mechanism for which mitochondrial functions are indispensable, and a fermentative pathway for which mitochondrial integrity is not required.

Suppression of maltose-negative phenotype by a specific nuclear gene (PMU1) in the petite cells of the yeast Saccharomyces cerevisiae

A small percentage of the primary petites isolated from strain 1403-7A-P1, constitutive for maltase synthesis, simultaneously lost the ability to utilize maltose and alpha-methylglucoside. Further studies showed that these primary petites were not stable with respect to maltose utilization. Approximately 30% of the secondary petites when isolated from the primary petites after vegetative growth were found to papillate on maltose plates. Tetrad analysis data revealed that a nuclear gene has reverted in these papillae, which is responsible for suppression of the maltose negative phenotype in primary petites. We have designated this nuclear gene as the PMU1 gene (petite maltose utilizer). The functional form of the PMU1 gene is required in addition to the MAL4 gene for both constitutive maltase synthesis and maltose utilization in cytoplasmic petite cells derived from strain 1403-7A-P1.