Figure 1.

Pathway describing sclareol and carotenoid biosynthesis in yeast. Erg20p catalyzes the formation of C₁₅ farnesyl pyrophosphate molecules (FPP) for isoprenoid and sterol biosynthesis. A variant (F96C) enzyme was previously engineered to catalyze geranylgeranyl pyrophosphate synthesis (GGPP). Fusion of ERG20 (F96C) to the Cistus creticus 8-hydroxy copalyl diphosphate synthase (CcCLS) generates 8-OH-CPP, which in turn is converted to sclareol either through spontaneous hydrolysis in the acidified culture medium or enzymatically by the Salvia sclarea sclareol synthase (SsSCLS). In carotenoid biosynthesis the inserted carotenogenic pathway cassette of X. dendrorhous expresses the the GGPP synthase (encoded by the crtE gene), the bifunctional enzyme phytoene synthase/lycopene cyclase (encoded by the crtYB gene) and phytoene desaturase (encoded by the crtI gene).