Threonine and methionine biosynthesis (WP423)

The biosynthesis of threonine and methionine in S. cerevisiae begins in a common three-step pathway that converts aspartate to homoserine. HOM3 and HOM2, which encode the enzymes responsible for the first and second steps of this pathway respectively, are regulated by Gcn4p under the general control of amino acid biosynthesis. Additionally, threonine represses HOM3 and competitively inhibits homoserine dehydrogenase (encoded by HOM6), lending that the flow of carbon into the common pathway is primarily regulated by threonine. The Hom3p, Hom2p, and Hom6p-catalyzed reactions yield homoserine, at which point the threonine and methionine pathways diverge. Phosphorylation of homoserine by homoserine kinase (encoded by THR1) directs homoserine towards the biosynthesis of threonine, whereas acetylation by homoserine O-transacetylase (encoded by MET2) commits homoserine to the biosynthesis of sulfur amino acids. Source: https://pathway.yeastgenome.org/

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