A Tryptophan 6-Halogenase and an Amidotransferase Are Involved in Thienodolin Biosynthesis

The biosynthetic gene cluster for the plant growth-regulating compound thienodolin was identified in and cloned from the producer organism Streptomyces albogriseolus MJ286-76F7. Sequence analysis of a 27 kb DNA region revealed the presence of 21 ORFs, 14 of which are involved in thienodolin biosynthesis. Three insertional inactivation mutants were generated in the sequenced region to analyze their involvement in thienodolin biosynthesis and to functionally characterize specific genes. The gene inactivation experiments together with enzyme assays with enzymes obtained by heterologous expression and feeding studies showed that the first step in thienodolin biosynthesis is catalyzed by a tryptophan 6-halogenase and that the last step is the formation of a carboxylic amide group catalyzed by an amidotransferase. The results led to a hypothetical model for thienodolin biosynthesis.