Fig. 3

Total biosynthesis of emodin (1), endocrocin (2) and their O-methylated derivatives in S. cerevisiae. Product profiles (HRMS ion chromatograms with the extracted m/z values of compounds 1, 2, 4, 5 and 6) from cultures of S. cerevisiae H6108 strains that: (A) express the genes for the selected nrPKSs of C. semisanguineus or C. sp. KIS-3; or (B) co-express the genes for CkPKS3 and the selected OMTs of C. semisanguineus or C. sp. KIS-3. The trace at the bottom of Panel B represents the overlay of extracted ion chromatograms for: authentic emodin (1), endocrocin (2), physcion (4), and dermolutein (5) standards. Culture extracts of the S. cerevisiae H6108 chassis are also shown in both panels. The extracted ion chromatograms (EICs) are m/z 269.044 [M–H]⁻ for (1); 313.038 [M–H]⁻ for (2); 283.062 [M–H]⁻ for physcion (4); 327.046 [M–H]⁻ for dermolutein (5); and 283.062 [M–H]⁻ for an uncharacterized O-methylemodin (6), possibly questin (8-O-methylemodin; a questin standard was not available and the yield of the metabolite was too low for isolation and structure elucidation)