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.