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Amatoxins, the lethal constituents of poisonous mushrooms in the genus Amanita, are bicyclic octapeptides. Two genes in A. bisporigera, AMA1 and PHA1, directly encode [alpha]-amanitin, an amatoxin, and the related bicyclic heptapeptide phallacidin, a phallotoxin, indicating that these compounds are synthesized on ribosomes and not by nonribosomal peptide synthetases. [alpha]-Amanitin and phallacidin are synthesized as proproteins of 35 and 34 amino acids, respectively, from which they are predicted to be cleaved by a prolyl oligopeptidase. AMA1 and PHA1 are present in other toxic species of Amanita section Phalloidae but are absent from nontoxic species in other sections. The genomes of A. bisporigera and A. phalloides contain multiple sequences related to AMA1 and PHA1. The predicted protein products of this family of genes are characterized by a hypervariable 'toxin' region capable of encoding a wide variety of peptides of 7-10 amino acids flanked by conserved sequences. Our results suggest that these fungi have a broad capacity to synthesize cyclic peptides on ribosomes. amanitin | cyclic peptide | phalloidin | phallotoxin | amatoxin

A molecular genetic analysis was done on HC-toxin biosynthesis to study the TOX loci of Cochliobolus and the evolution of new pathogens. Results show a 22 kilobase chromosomal region containing a 15.7 kilobase open reading frame encoding a multifunctional cyclic peptide synthase. Furthermore, it was shown that this enzyme is encoded in TOX2 and the evolution of the host range in C. carbonum includes the insertion or deletion of a large piece of chromosomal DNA.