Based on the results of mapping of ggt , eight strains were selected from a gene library of E. coli . One of the strains harboring pLC9-12 was found to show 14 times higher γ-glutamyltranspeptidase activity per cell than the wild type strain. The ggt was subcloned to the Bam HI site of pUC18 and the recombinant plasmid sSH101 was obtained. Ggt − phenotype of γ-glutamyltranspeptidase-deficient mutants was complemented by pSH101. The specific activity of the enzyme in cells harboring pSH101 was 37-fold higher than that in the wild type cells. γ-Glutamyltranspeptidase was isolated from the periplasmic fraction of the cells by simple two steps and crystallized.