of the applicant): Filamentous fungi are the richest known source of polyketides, secondary metabolites of proved pharmaceutical value that possess enormous potential for identification of new drugs. The goal of this proposal is to adapt recently developed genetic technology to fungi, with the aim of producing many novel polyketides to be screened for desirable pharmaceutical properties. Our primary fungus is the genetically tractable ascomycete Cochliobolus heterostrophus, whose unique polyketide synthase-encoding gene (PKS1) contains a complete set of biosynthetic domains. Its predominant polyketide (T-toxin) is a large (C41) linear molecule whose structure provides abundant opportunities for modification via genetic engineering. In phase I we will determine if novel polyketides can be produced by expressing native or engineered PKS1 either in a PKS1-deletion strain of C. Heterostrophus or in the heterologous fungal host Aspergillus nidulans. A. nidulans is known to produce polyketides, but not T-toxin. In Phase II the same two hosts will be used for expression of thousands of chimeric PKS genes, generated with a new combinatorial chemistry procedure that will mix and match enzymatic domains chosen from a variety of bacterial and fungal sources. All transgenic strains will be screened for desirable polyketides, using more than 100 proprietary bioassays.
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