Anthracyclines are tetracyclic aromatic polyketides produced by a type II iterative polyketide synthase. Biologically active anthracyclines are glycosylated with deoxy- and aminodeoxysugars. Most of the biosynthetic gene clusters for daunorubicin, doxorubicin, aclacinomycin and nogalamycin biosynthesis have been cloned and sequenced, and functions of many individual open reading frames have been determined experimentally and by sequence comparisons.