Non-reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of orsellinic acid, as well as of the cathepsin K inhibitors F9775 A and F9775 B (PubMed:19666480, PubMed:20174687). The non-reducing polyketide synthase orsA produces orsellinic acid by condensing acetyl-CoA with 3 malonyl-CoA units (PubMed:19666480, PubMed:20174687). Further modifications by the decarboxylase orsB and the tyrosinase-like protein orsC lead to the production of F9775 A and F9775 B (PubMed:20174687). The functions of orsD and orsE remain unclear since only orsB and orsC are required to convert orsellinic acid into F9775 A and F9775 B (PubMed:20174687). acetyl-CoA + 2 H(+) + 3 malonyl-CoA = 3 CO2 + 4 CoA + orsellinate Secondary metabolite biosynthesis. Expression is induced by an intimate physical interaction of the fungal mycelia with the bacterium Streptomyces hygroscopicus (PubMed:19666480). Expression is repressed by VeA and MvlA via histone 3 acetylation by the SAGA/ADA complex (PubMed:23892751, PubMed:23841751). Multidomain protein; including a starter unit:ACP transacylase (SAT) that selects the starter unit; 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 product template (PT) domain that controls the immediate cyclization regioselectivity of the reactive polyketide backbone; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm (By similarity). The release of the polyketide chain from the non-reducing polyketide synthase is mediated by the thioesterase (TE) domain localized at the C-ter of the protein (By similarity). Abolishes the production of orsellinic acid, lecanoric acid and F-9775A/B (PubMed:19666480, PubMed:20174687).