A novel hexaketide naphthalene synthesized by a chimeric polyketide synthase composed of fungal pentaketide and heptaketide synthases

Aspergillus nidulans wA and Colletotrichum lagenarium pks1 code for iterative type I polyketide synthases (PKSs) and synthesize heptaketide naphthopyrone and pentaketide naphthalene, respectively. A chimeric PKS, called SW-B, composed of WA and PKS1 synthesized mainly hexaketide isocoumarin and an unknown yellow compound. The latter was identified as the novel hexaketide 2-acetyl-1,3,6,8-tetrahydroxynaphthalene. These findings indicate broad substrate specificity of the WA C-terminal domain for Claisen-type cyclization and an unprecedented chain length determination mechanism of fungal aromatic PKSs.