MCH4 is a multicopy suppressor of glycine toxicity in Saccharomyces cerevisiae

Saccharomyces cerevisiae can either import amino acids from the surrounding or synthesize inside the cell, and both processes are tightly regulated. Disruption of such regulation can result in amino acid toxicity to the cell through mechanisms that are poorly understood. In this study we make use of a mutant strain with deregulated general amino acid permease gene whose growth is inhibited by low concentrations of several amino acids. We carry out multicopy suppression screen with several toxic amino acids and identify MCH4 as a gene that suppresses inhibitory effects of glycine. We find that expression of MCH4 is regulated by osmotic shock but not other kinds of stress. These findings are discussed in the context of possible mechanisms of amino acid toxicity.