Interdomain Coordination Determines Polyketide Extender Unit Specificity in UK‐2A Biosynthesis

Controlling the incorporation of extender units is a key strategy for manipulating polyketide scaffolds. Current understanding suggests that extender unit incorporation by modular polyketide synthase (PKS) is primarily regulated by acyltransferase domains, along with ketosynthase, ketoreductase, and thioesterase domains. In this study, the mechanism is investigated underlying the specific incorporation of the benzyl side chain at the C7 position of UK‐2A, both in vivo and in vitro. These findings reveal that the incorporation of the benzylmalonyl‐CoA extender unit is governed by interdomain coordination across the entire PKS module, rather than being controlled by individual domains. These results challenge previous recognition and offer new insights for the future engineering of polyketides.