Adenosine kinase-deficient mutant of Saccharomyces cerevisiae accumulates S-adenosylmethionine because of an enhanced methionine biosynthesis pathway

To isolate an S-adenosylmethionine (SAM)-accumulating yeast strain and to develop a more efficient method of producing SAM, we screened methionine-resistant strains using the yeast deletion library of budding yeast and isolated 123 strains. The SAM content in 81 of the 123 strains was higher than that in the parental strain BY4742. We identified ADO1 encoding adenosine kinase as one of the factors participating in high SAM accumulation. The Xa dagger ado1 strain that was constructed from the X2180-1A strain (MAT a, ATCC 26786) could accumulate approximately 30-fold (18 mg/g dry cell weight) more SAM than the X2180-1A strain in yeast extract peptone dextrose medium. Furthermore, we attempted to identify the molecular basis underlying the differences in SAM accumulation between Xa dagger ado1 and X2180-1A strains. DNA microarray analysis revealed that the genes involved in the methionine biosynthesis pathway, phosphate metabolism, and hexose transport were mainly overexpressed in the Xa dagger ado1 strain compared with the X2180-1A strain. We also determined the levels of various metabolites involved in the methionine biosynthesis pathway and found increased content of SAM, tetrahydrofolate (THF), inorganic phosphate, polyphosphoric acid, and S-adenosylhomocysteine in the Xa dagger ado1 strain. In contrast, the content of 5-methyl-THF, homocysteine, glutathione, and adenosine was decreased. These results indicated that the a dagger ado1 strain could accumulate SAM because of preferential activation of the methionine biosynthesis pathway.