A STUDY OF BRANCHED-CHAIN AMINO-ACID AMINOTRANSFERASE AND ISOLATION OF MUTATIONS AFFECTING THE CATABOLISM OF BRANCHED-CHAIN AMINO-ACIDS IN SACCHAROMYCES-CEREVISIAE

The specific activity of branched-chain amino acid aminotransferase wa s highest when S. cerevisiae was grown in minimal medium containing a branched-chain amino acid as nitrogen source. Growth in complex media with glycerol or ethanol gave moderately high levels, whereas with glu cose and fructose the specific activity was very low. Mutagenesis defi ned three genes (BAA1 to BAA3) required for branched-chain amino acid catabolism. The baa1 mutation reduced the specific activity of the ami notransferase, the stationary phase density in YEPD and caused gross m orphological disturbance. Branched-chain amino acid aminotransferase i s essential for sporulation.