A series of gene inactivation and gene recombination experiments involving oxygenase encoding genes of the gilvocarcin and jadomycin biosynthetic pathways showed that the enigmatic oxidative rearrangement cascades in these pathways is catalyzed by multi-oxygenase complexes and follows almost identical paths up through the C-C bond cleavage reaction. The two pathways branch beyond this key reaction and end up eventually in the unique tetracyclic benzo[d]naphtho[1,2-b]pyran-6-one and pentacyclic benz[b]oxazolophenanthridine backbones, respectively, typical for these groups of anticancer antibiotics.