The biosynthetic gene cluster for the pyralomicin antibiotics has been cloned and sequenced from Nonomuraea spiralis IMC A-0156. The 41 kb gene cluster contains 27 ORFs predicted to encode all of the functions for pyralomicin biosynthesis. This includes nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) required for the formation of the benzopyranopyrrole core unit, as well as a suite of tailoring enzymes (e.g., four halogenases, an O-methyltransferase, and an N-glycosyltransferase) necessary for further modifications of the core structure. The N-glycosyltransferase is predicted to transfer either glucose or a pseudosugar (cyclitol) to the aglycone. A gene cassette encoding C7-cyclitol biosynthetic enzymes was identified upstream of the benzopyranopyrrole-specific ORFs. Targeted disruption of the gene encoding the N-glycosyltransferase, prlH, abolished pyralomicin production, and recombinant expression of PrlA confirms the activity of this enzyme as a sugar phosphate cyclase involved in the formation of the C7-cyclitol moiety.
