Chemical modularity in building fungal polyketides. A) Representative molecules. The red portion indicates reduced products of upstream synthases that are transferred to downstream NR-PKSs. B) Proposed biosynthesis of chaetoviridin A (6) and chaetomugilin A (7). Domain abbreviations:ketosynthase (KS), malonyl-CoA:acyl carrier protein acyltransferase (MAT), dehydratase (DH), methyltransferase (MT), enoylreductase (ER), ketoreductase (KR), acyl carrier protein (ACP), starter-unit:ACP-transacylase (SAT), product template (PT), and reductive domain (R). 11-SNAC was synthesized and used to directly load the KS of CazM.