Large chromosomal DNAfragments containing different parts of the putative rubromycin polyketide synthase "gene cluster were cloned and functionally expressed in S. coelicolor CH999. Expression of these clones yielded 5-10 metabolites that were not detected in S. collinus culture extracts. This paper focusses on one of the new metabolites, termed collinone, that was isolated in large quantities and purified for spectroscopic structure determination and biological screening assays. Collinone is a heavily oxidized angular hexacyclic compound