<jats:title>Abstract</jats:title><jats:p><jats:bold>More than meets the I</jats:bold>: The biosynthetic gene cluster for indanomycin was identified from <jats:italic>Streptomyces antibioticus</jats:italic> NRRL 8167. The framework of the indanomycins includes a tetrahydropyran and a central indane ring system. The final module of the indanomycin polyketide synthase possesses an unusual terminal module lacking an integrated thioesterase.<jats:boxed-text content-type="graphic" position="anchor"><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/mcontent.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:boxed-text><jats:p><jats:italic>Metabolites that harbor a core indane scaffold are found to have diverse biological properties. Indanomycin and related pyrroloketoindanes are ionophores and have demonstrated antiparasitic, insecticidal, and antibacterial activities. To understand the biochemical mechanisms guiding formation of the central indane ring, the biosynthetic gene cluster for indanomycin was identified from</jats:italic> Streptomyces antibioticus <jats:italic>NRRL 8167 and sequenced to ∼80 kb; this revealed five genes encoding subunits of a polyketide synthase (PKS) and 18 other open reading frames. The involvement of this cluster in indanomycin biosynthesis was confirmed by deletion mutagenesis. The indanomycin PKS lacks the expected thioesterase at the carboxy terminus of the final module, and instead appears to house an incomplete module containing an unusual cyclase domain. These findings now enable additional detailed genetic and biochemical studies of the mechanisms guiding the generation of pyrroloketoindanes.</jats:italic>