“…[9][10][11][12] Another class of PKS, the polyene PKS that has been studied for less than a decade, has every domain from the FAB elongation cycle except the ER domain, producing polyene [13][14][15][16] or aryl polyene products. [17][18][19][20][21][22][23] In terms of substrate shuttling, the polyene PKS system is more similar to the FAS system where ACP is required to deliver substrates to multiple enzymes during elongation. Although various nomenclatures have been used to describe the two PKS systems mentioned above, for example, by their product types (aromatic vs. polyene) or the reduction level (nonreducing vs. highly reducing), in this review, we will refer to them by their elongation intermediates, polyketone and polyene, respectively, for simplicity.…”