PKSE domain organization and role in enediyne core biosynthesis. (A) Domain organization of PKSE is similar to that of the PUFA synthases. (B) Enediyne core biosynthesis carried out by PKSE and accessory enzymes is responsible for divergence of the polyketide intermediate into either 9- or 10-membered enediyne families of natural products. (C) Structure of the polyene product 1,3,5,7,9,11,13-pentadecaheptanene isolated upon coexpression of 9-membered pksE and pksE10 exemplified by sgcE/sgcE10 and ncsE/ncsE10.