Abstract
YAL044, a gene on the left arm of Saccharomyces cerevisiae chromosome one, is shown to code for the H-protein subunit of the multienzyme glycine cleavage system. The gene designation has therefore been changed to GCV3, reflecting its role in the glycine cleavage system. GCV3 encodes a 177-residue protein with a putative mitochondrial targeting signal at its amino terminus. Targeted gene replacement shows that GCV3 is not required for growth on minimal medium; however, it is essential when glycine serves as the sole nitrogen source. Studies of GCV3 expression revealed that it is highly regulated. Supplementation of minimal medium with glycine, the glycine cleavage system's substrate, induced expression at least 30-fold. In contrast, and consistent with the cleavage of glycine providing activated single-carbon units, the addition of the metabolic end products that require activated single-carbon units repressed expression about 10-fold. Finally, like many amino acid biosynthetic genes, GCV3 is subject to regulation by the general amino acid control system.
Highlights
The glycine cleavage system, a multienzyme complex consisting of four different subunits (P, H, T, and L-proteins), catalyzes the oxidative cleavage of glycine into CO2 and NH3
Genetic analysis has shown that no single mechanism is essential for the production of 5,10-MTHF [13]; inactivation of both glycine hydroxymethyltransferase and glycine cleavage system-dependent 5,10-MTHF synthesis renders S. cerevisiae growth contingent upon supplementation with formate [14]
Mutants blocked in the synthesis of serine from 3-phosphoglycerate can use glycine to provide both C1 units via the glycine cleavage system and serine via the reaction catalyzed by glycine hydroxymethyltransferase (Fig. 1)
Summary
Functional role of the GCV3 gene and to delineate the general features of its regulation. We show that GCV3, a gene identified by the systematic sequencing of chromosome one [22], codes for an H-protein that is essential for glycine cleavage. Studies of GCV3 expression revealed that it is induced by glycine and repressed by the metabolic products that require C1 units for their synthesis. GCV3 is subject to regulation by the general amino acid control system
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