Bacterial genomes often contain clusters of genes involved in secondary metabolite biosynthesis, that are not expressed until induction by specific chemical or physical stimuli. In an Advanced Online Publication in
Genome sequence tags (GSTs) were screened against a database of microbial gene clusters of metabolic loci to rapidly identify novel metabolic loci. Zazopoulus et al. used the genome scanning approach to screen actinomycetes strains for genes involved in the biosynthesis of enedyine, a class of anti-tumor antibiotics. They identified a conserved cluster of five genes — the putative "warhead gene cassette" — including a polyketide synthase gene that may be involved in the formation of the reactive chromophore ring structures found in all enediynes.