Characterization of a partial duplication of the aflatoxin gene cluster in Aspergillus parasiticus ATCC 56775

A partial duplication of the complete aflatoxin gene cluster containing homologues of aflR-aflJ-adhA-estA-norA-ver1 and omtB was identified from Aspergillus parasiticus ATCC 56775. The genes, verA-avnA-verB-avfA, between ver1 and omtB in the complete gene cluster. however, were not found. One-hybrid assays showed that the duplicated aflR gene (aflR2) encoded a protein that could activate transcription just as that encoded by aflR1, the aflR gene in the complete gene cluster. Two-hybrid assays showed that AFLR2 also interacted with a putative coactivator. AFLJ1, at comparable levels to AFLR1. Deletion of aflR1 resulted in the loss of production of aflatoxin precursors, which suggested that aflR2 could not completely replace the function of aflR1. Point mutations found in adhA2, pre-termination in ver1B and norA2, and a large deletion in omtB2 probably render these duplicated genes to become nonfunctional. A close examination of the history of isolates reported to have a partial duplication suggested that duplication of the aflatoxin cluster is not a prevalent event.