Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of 1233A, a natural compound known as an inhibitor of HMG-CoA synthase in the mevalonate pathway and with antibacterial and antifungal activities (PubMed:32139880). The highly reducing polyketide synthase g433 gene is responsible for the 1233A backbone biosynthesis and the cytochrome P450 monoxygenase g430 catalyzes oxidation of the backbone (Probable). Mycotoxin biosynthesis. Expression is increased upon exposure to hygromycin B. Multidomain protein; including a ketosynthase (KS) that catalyzes repeated decarboxylative condensation to elongate the polyketide backbone; a malonyl-CoA:ACP transacylase (MAT) that selects and transfers the extender unit malonyl-CoA; a dehydratase (DH) domain that reduces hydroxyl groups to enoyl groups; a methyltransferase (CMeT) domain responsible for the incorporation of methyl groups; an enoylreductase (ER) domain that reduces enoyl groups to alkyl group; a ketoreductase (KR) domain that catalyzes beta-ketoreduction steps; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm. Impairs the ability to produce 1233A and its hydrolysis product 1233B.