Figure 1. A complete module from the spinosyn PKS.
(a) Domain composition of the second module of the spinosyn PKS (SpnMod2) and location of the Spn(KR+ER)2 didomain (approximate sequence scale). KS, ketosynthase; AT, acyltransferase; DH, dehydratase; KRs, ketoreductase structural subdomain; ER, enoylreductase; KRc, ketoreductase catalytic subdomain; ACP, acyl carrier protein. (b) The indicated methylene group in the spinosyn backbone is generated by the processing enzymes in SpnMod2. (c) The complex polyketides spinosyn A and spinosyn D comprise the insecticide spinosad.