Figure 1.

Overview of the CARD modules. CARD I: module connecting yeast sterol metabolism with the initial cardenolide pathway; CARD II (as described above): module comprising the five steps of the cardenolide pathway leading from pregnenolone to 5β‐pregnane‐3β,21‐diol‐20‐one; CARD III: module allowing for C‐14β‐hydroxylation and butenolide ring formation. 1) The fusion gene ADR/ADX was omitted at this stage to further investigate its benefit in the CYP21A1 step. 3βHSD, Δ5‐3β‐hydroxysteroid dehydrogenase; 3KSI, steroid Δ5‐isomerase; ADR, adrenodoxin reductase; ADX, adrenodoxin; CYP21A1, steroid 21‐hydroxylase; St5βR, steroid‐5β‐reductase