ABSTRACTThe fungusThelonectria discophoraSANK 18292 produces the iminosugar nectrisine, which has a nitrogen-containing heterocyclic 5-membered ring and acts as a glycosidase inhibitor. In our previous study, an oxidase (designated NecC) that converts 4-amino-4-deoxyarabinitol to nectrisine was purified fromT. discophoracultures. However, the genes required for nectrisine biosynthesis remained unclear. In this study, the nectrisine biosynthetic gene cluster inT. discophorawas identified from the contiguous genome sequence around thenecCgene. Gene disruption and complementation studies and heterologous expression of the gene showed thatnecA,necB, andnecCcould be involved in nectrisine biosynthesis, during which amination, dephosphorylation, and oxidation occur. It was also demonstrated that nectrisine could be produced by recombinantEscherichia colicoexpressing thenecA,necB, andnecCgenes. These findings provide the foundation to develop a bacterial production system for nectrisine or its intermediates through genetic engineering.IMPORTANCEIminosugars might have great therapeutic potential for treatment of many diseases. However, information on the genes for their biosynthesis is limited. In this study, we report the identification of genes required for biosynthesis of the iminosugar nectrisine inThelonectria discophoraSANK 18292, which was verified by disruption, complementation, and heterologous expression of the genes involved. We also demonstrate heterologous production of nectrisine by recombinantE. coli, toward developing an efficient production system for nectrisine or its intermediates through genetic engineering.