The met17 mutation prevents assimilation of sulfate. Combination of met6, mht1 and sam4 prevents methylation of homocysteine into methionine. The sam1 and sam2 mutations inactivate the two genes encoding methionine-adenosyltransferase (also known as SAM synthetase), preventing SAM biosynthesis from methionine. The cys4 mutation inactivates cystathionine--synthase and blocks the transsulfuration pathway ensuring conversion of homocysteine (Hcy) into cysteine. The gsh1 mutation prevents GSH biosynthesis.
