A major challenge in previous reconstitution attempts was the catalytic promiscuity of T5αH, which led to the formation of multiple byproducts, complicating the pathway. This paper successfully addressed this issue by tuning the expression levels of T5αH using different promoters. By lowering T5αH expression with weaker promoters (like UBQ10 and NOS promoters), the formation of overoxidized byproducts was significantly reduced, and the yield of taxadien-5α-ol, a key precursor to paclitaxel, was increased by three-fold. This allowed for a more streamlined biosynthetic pathway with fewer side-products.