Ansaseomycins are ansamycin-type natural products produced through expression of the asm gene cluster in a heterologous host. A rare berberine bridge enzyme (BBE) like oxidase, AsmF, is encoded in the asm gene cluster. Deletion of asmF led to the accumulation of a series of structurally diverse compounds, all of which lacked the 23-hydroxyl group in naphthalenic motif. Our work demonstrated that AsmF dictated the formation of the naphthalenic hydroxyl group in ansaseomycin biosynthesis.

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