Sweet ways: We have investigated the glycosyltransferase genes of the saquayamycin Z (shown) and galtamycin B biosynthetic gene cluster from Micromonospora sp. Tü6368. The results unambiguously show that both compounds are derived from the same cluster. Furthermore, the function of five glycosyltransferases was elucidated, and the results have shed light on the assembly of the sugar chains.The Gram-positive bacterium, Micromonospora sp. Tü6368 produces the angucyclic antibiotic saquayamycin Z and the tetracenequinone galtamycin B. The structural similarity of both compounds suggests a common biosynthetic pathway. The entire biosynthetic gene cluster (saq gene cluster) was cloned and characterized. DNA sequence analysis of a 36.7 kb region revealed the presence of 31 genes that are probably involved in saquayamycin Z and galtamycin B formation. Heterologous expression experiments and targeted gene inactivations were carried out to specifically manipulate the saquayamycin Z and galtamycin B pathways; this demonstrated unambiguously that both compounds are derived from the same cluster. The inactivation of glycosyltransferase genes led to the production of novel saquayamycin and galtamycin derivatives, provided information on the assembly of the sugar chains, and showed that tetracenequinones are formed from angucyclines.