Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of the lipopeptide fusaristatin A (PubMed:25412204). Fusaristatin A consists of a polyketide chain linked to three amino acid residues glutamine (Gln), dehydroalanine (dehydro-Ala), and beta-aminoisobutyric acid (PubMed:25412204). The biosynthesis starts with formation of a linear polyketide chain by the highly reducing polyketide synthase PKS6 (PubMed:25412204). The gene cluster does not contain an acyl-CoA ligase or an acyl-transferase, and it is therefore predicted that the polyketide is transferred directly to the nonribosomal peptide synthetase NRPS7 (Probable). Modules 1-3 from NRPS7 incorporate dehydro-Ala, Gln, and beta-aminoisobutyric acid in the compound, which is released by cyclization (PubMed:25412204). The beta-aminoisobutyric acid units are most likely not freely available to the NRPS, but can be synthesized from thymine, which requires a dehydrogenase, a monooxygenase, and an aminotransferase. The fusaristatin A cluster contains a cytochrome P450 monooxygenase (FGSG_08207) and an aminotransferase (FGSG_17085), which theoretically can perform two of the enzymatic steps (Probable). The enzymes may however also be involved in biosynthesis of dehydroalanine or modification of the polyketide (Probable). The dehydro-Ala residue can be a result of cyclization, where serine is dehydrated (Probable). The last gene of the cluster encodes a protein with an A/B barrel domain found in variable enzymes, which hampers functional prediction (Probable). Secondary metabolite biosynthesis. 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 production of fusaristatin A.