Xantholipin isolated from Streptomyces flavogriseus is a hexacyclic aromatic polyketide with potent antitumor activity.Previous studies have cloned its biosynthetic gene cluster,which consists of 49 open reading frames.19 redox genes were identified by bioinformatics analysis, consistent with the highly oxidized structure of xantholipin.Several important tailoring enzymes were characterized by in-frame mutagenesis and/or in vitro enzymatic analysis.