Autocatalytic backbone N-methylation in a family of ribosomal peptide natural products

Characterization of the gene cluster for omphalotin biosynthesis reveals that they are ribosomally synthesized peptides whose internal α- N -methyl groups are installed by a methyltransferase fused to the precursor peptide substrate. Peptide backbone N-methylation, as seen in cyclosporin A, has been considered to be exclusive to nonribosomal peptides. We have identified the first post-translationally modified peptide or protein harboring internal α-N-methylations through discovery of the genetic locus for the omphalotins, cyclic N-methylated peptides produced by the fungus Omphalotus olearius . We show that iterative autocatalytic activity of an N -methyltransferase fused to its peptide substrate is the signature of a new family of ribosomally encoded metabolites.