Properties of revertants of lys2 and lys5 mutants as well as alpha-aminoadipate-semialdehyde dehydrogenase from Saccharomyces cerevisiae.

alpha-Aminoadipate-semialdehyde dehydrogenase catalyzes the conversion of alpha-aminoadipate to alpha-aminoadipate-semialdehyde in the biosynthetic pathway of lysine in yeasts and molds. Mutants belonging to lys2 and lys5 loci of Saccharomyces cerevisiae lacked the alpha-aminoadipate-semialdehyde dehydrogenase activity. Complementation in vitro was demonstrated by combining the extracts from different lys2 and lys5 mutants. Some of the revertants of lys2 and lys5 mutants exhibited lower specific activity and higher thermolability of alpha-aminoadipate-semialdehyde dehydrogenase than the enzyme from wild-type cells. The enzyme was partially purified from wild-type cells and the molecular weight of the enzyme was estimated on a Sephacryl S-300 column at 180,000. Results from the revertant analysis and in vitro complementation indicated LYS2 and LYS5 as structural genes, each encoding a subunit of this large enzyme.