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sai-1 Mutation in Saccharomyces cerevisiae: Characteristics of Inhibition by S-Adenosylmethionine and S-Adenosylhomocysteine and Protection by Methionine

¹ Department of Bacteriology and Public Health, Washington State University, Pullman, Washington 99163, and Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680

ABSTRACT

The relationship of methionine to the inhibition caused by S-adenosylmethionine and S-adenosylhomocysteine in strains containing the sai-1 mutation has been investigated and shown to affect indirectly the survival of the mutants. The ability of the mutants to take up both inhibitors is similar to that of the wild-type cells. The mutant also retains the ability to hydrolyze S-adenosylhomocysteine and incorporate the hydrolytic products into the various cellular fractions. Maximal inhibition of the sai-1 mutants occurs at an extracellular concentration of 0.005 mMS-adenosylmethionine and 0.025 to 0.05 mMS-adenosylhomocysteine when the cellular concentration is 0.05 mg (dry weight) per ml. The results suggest that the sai-1 mutation affects reaction(s) either not associated with methionine biosynthesis, or methionine synthesis and at least one other critical cellular function.