Identification of a Gene Involved in the Synthesis of a Dipeptidyl Peptidase IV Inhibitor in Aspergillus oryzae

WYK-1 is a dipeptidyl peptidase IV inhibitor produced byAspergillus oryzae strain AO-1. Because WYK-1 is an isoquinoline derivative consisting of threel -amino acids, we hypothesized that a nonribosomal peptide synthetase was involved in its biosynthesis. We identified 28 nonribosomal peptide synthetase genes in the sequenced genome ofA. oryzae RIB40. These genes were also identified in AO-1. Among them, AO0900019 (wykN ) was specifically expressed under WYK-1-producing conditions in AO-1. Therefore, we constructedwykN gene disruptants of AO-1 after nonhomologous recombination was suppressed by RNA interference to promote homologous recombination. Our results demonstrated that the disruptants did not produce WYK-1. Furthermore, the expression patterns of 10 genes downstream ofwykN were similar to the expression pattern ofwykN under several conditions. Additionally, homology searches revealed that some of these genes were predicted to be involved in WYK-1 biosynthesis. Therefore, we propose thatwykN and the 10 genes identified in this study constitute the WYK-1 biosynthetic gene cluster.