Involved in the biosynthesis of aklavinone which is an important precursor common to the formation of the clinically significant anthracyclines such as carminomycin, daunorubicin (daunomycin), rhodomycin, aclacinomycin T (aklavin) and aclacinomycin A (aclarubicin). These compounds are aromatic polyketide antibiotics that exhibit high cytotoxicity and are widely applied in the chemotherapy of a variety of cancers. Catalyzes the cyclization of aklanonic acid methyl ester to yield aklaviketone. methyl aklanonate = aklaviketone Optimum pH is between 6 and 7.5. Antibiotic biosynthesis; daunorubicin biosynthesis. Antibiotic biosynthesis; carminomycin biosynthesis. Antibiotic biosynthesis; rhodomycin biosynthesis. Antibiotic biosynthesis; aclacinomycin biosynthesis. Homotetramer. Cells lacking this gene accumulate aklanonic acid methyl ester. Belongs to the polyketide cyclase DnrD family.