Oxidase ustYa is involved in the production of ustiloxins, toxic cyclic peptides, in fungi. Ustiloxins were found to be the first example of cyclic peptidyl secondary metabolites that are ribosomally synthesized in filamentous fungi. The homologous genes ustYa and ustYb (which are found in the gene cluster for ustiloxins) have been shown to be involved in cyclization of the peptide.

1: Characterization of the biosynthetic gene cluster for the ribosomally synthesized cyclic peptide ustiloxin B in Aspergillus flavus. Umemura M, Nagano N, Koike H, Kawano J, Ishii T, Miyamura Y, Kikuchi M, Tamano K, Yu J, Shin-ya K, Machida M; Fungal Genet Biol. 2014;68:23-30. PMID:24841822