Alanine : glyoxylate aminotransferase of Saccharomyces cerevisiae –encoding gene AGX1 and metabolic significance

Alanine : glyoxylate aminotransferase is one of three different enzymes used for glycine synthesis in Saccharomyces cerevisiae . The open reading frame YFL030w (named AGX1 in the following), encoding this enzyme, was identified by comparing enzyme specific activities in knockout strains. While 100% activity was detectable in the parental strain, 2% was found in a YFL030w:: kanMX4 strain. The ORF found at that locus was suspected to encode alanine : glyoxylate aminotransferase because its predicted amino acid sequence showed 23% identity to the human homologue. Since the YFL030w:: kanMX4 strain showed no glycine auxtrophic phenotype, AGX1 was replaced by KanMX4 in a Δ GLY1 Δ SHM1 Δ SHM2 background. These background mutations, which cause inactivation of threonine aldolase, mitochondrial and cytosolic serine hydroxymethyltransferase, respectively, lead to a conditional glycine auxotrophy. This means that growth is not possible on glucose but on ethanol as the sole carbon source. Additional disruption of AGX1 revealed a complete glycine auxotrophy. Complementation was observed by transformation with a plasmid‐encoded AGX1 . Copyright © 2003 John Wiley & Sons, Ltd.