The GLY1 Gene of Saccharomyces Cerevisiae Encodes a Low-Specific L-threonine Aldolase that Catalyzes Cleavage of L-allo-Threonine and L-threonine to Glycine

Expression of the Gene in Escherichia Coli and Purification and Characterization of the Enzyme


H. Yamada, Toyama Prefectural University, Kurokawa 5180, Kosugi City, Toyama, Japan 939-03
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The GLY1 gene of Saccharomyces cerevisiae is required for the biosynthesis of glycine for cell growth [McNeil, J. B., McIntosh, E. V., Taylor, B. V., Zhang, F.-R., Tang, S. & Bognar, A. L. (1994)J. Biol. Chem. 269, 9155–9165], but its gene product has not been identified. We have found that the GLY1 protein is similar in primary structure to L-allo-threonine aldolase of Aeromonas jandiae DK-39, which stereospecifically catalyzes the interconversion of L-allo-threonine and glycine. The GLY1 gene was amplified by PCR, with a designed ribosome-binding site, cloned into pUC118, and expressed in Escherichia coli cells. The enzyme was purified to homogeneity, as judged by polyacrylamide gel electrophoresis. The enzyme has a molecular mass of about 170 kDa and consists of four subunits identical in molecular mass. The enzyme contains 2 mol pyridoxal 5′-phosphate/4 mol of subunit as a cofactor, and its absorption spectrum exhibits maxima at 280 nm and 420 nm. The enzyme catalyzes the cleavage of not only L-allo-threonine to glycine but also L-threonine. We have termed the enzyme a low-specific L-threonine aldolase to distinguish it from L-allo-threonine aldolase.