The role of amino acids and Gcn4p in the shift of Saccharomyces cerevisiae from anaerobic to aerobic conditions

Abstract

Brewing conditions for commercial alcohol production have been extensively studied and optimized; yet less is known about the metabolism of Saccharomyces cerevisiae under brewing conditions. In brewing, anaerobically stored yeast are pitched into aerated wort. Aeration is vital for subsequent anaerobic yeast growth and metabolism; however, cellular adaptation is necessary to counter the stress experienced during this shift. The transcriptional activator Gcn4p is considered the master regulator of amino acid metabolism in S. cerevisiae and is required for the transcriptional response to amino acid starvation. Here it is shown that Gcn4p plays a previously undescribed role in regulating adaptation to anaerobic growth. A gcn4 mutant exhibited a highly extended lag phase after a shift to anaerobiosis that was the result of L-serine depletion. In addition, Bas1p, the transcriptional regulator of the one-carbon metabolism and purine biosynthesis was strictly required for anaerobic growth and this was similarly due to L-serine limitation in bas1 mutants. The induction of one-carbon metabolism during anaerobiosis is needed to increase the supply of L-serine from the glycine and threonine pathways. Using a number of experimental approaches, we demonstrate that these transcription regulators play vital roles in regulating L-serine biosynthesis in the face of increased demand during adaptation to anaerobiosis. This increased L-serine requirement is most likely due to anaerobic remodelling of the cell wall, involving de novo synthesis of a large number of very serine-rich mannoproteins and an increase in the total serine content of the cell wall. Interestingly, during anaerobic starvation for Lserine, this essential amino acid is preferentially directed to the cell wall, indicating the existence of a regulatory mechanism to balance competing cellular demands.

Date of Award	2009
Original language	English