The Claviceps purpurea Gene Encoding Dimethylallyltryptophan Synthase, the Committed Step for Ergot Alkaloid Biosynthesis

The first pathway-specific step of ergot alkaloid biosynthesis in the fungus, Claviceps purpurea, is catalyzed by the prenyltransferase, 4-(γ,γ-dimethylallyl)tryptophan synthase. Partial sequence information was obtained for the purified enzyme and a degenerate oligonucleotide mixture was used to identify and amplify segments of the gene, dmaW. The complete gene and near-full-length cDNA were cloned and sequenced. The cDNA was cloned in a yeast expression vector in sense and antisense orientations relative to the inducible GAL1 promoter. Extracts of yeast transformants with the sense constructs, but not antisense constructs or cloning vector, catalyzed production of 4-(γ,γ-dimethylallyl)tryptophan. The sequence of dmaW and its cDNA indicated that it encoded a 455 amino acid polypeptide with a predicted molecular mass of 51,824 Da and a putative prenyl diphosphate binding motif.