S. cerevisiae sake K6 was the firstly isolated industrial strain to overproduce S-adenosyl-L-methionine (SAM). Although the strain has advantages over other strains, such as GRAS (generally recognized as safe) property, the S. cerevisiae K6 has not been further developed with DNA recombinant technology due to the lack of a proper genetic marker. In this study, UV mutagenesis was conducted with S. cerevisiae sake K6. With the method, a mutant of sake yeast with leucine auxotroph, K6-1, was isolated. The mutant showed comparable growth rate and SAM productivity with its wild type. Using the auxotroph as a genetic marker, a SAM synthase in S. cerevisiae, SAM2, was overexpressed in the mutant strain. This recombinant DNA technology successfully increased SAM productivity in sake yeast.