CONSERVATION OF STRUCTURE AND FUNCTION OF THE AFLATOXIN REGULATORY GENE AFLR FROM ASPERGILLUS-NIDULANS AND ASPERGILLUS-FLAVUS

Under limiting growth conditions, Aspergillus nidulans produces a carc inogenic secondary metabolite related to aflatoxin and called sterigma tocystin (ST). The genes for ST biosynthesis are co-ordinately regulat ed and are all found within an approximately 60-kilobase segment of DN A. One of the genes within this region is predicted to encode a CX2CX6 CX6CX2CX6CX2 zinc binuclear cluster DNA-binding protein that is relate d to the Aspergillus flavus and Aspergillus parasiticus aflatoxin regu latory gene aflR. Deletion of the A. nidulans aflR homolog resulted in an inability to induce expression of genes within the ST gene cluster and a loss of ST production. Because A. nidulans aflR mRNA accumulate s specifically under conditions that favor ST production we expect tha t activation of ST biosynthetic genes is determined by A. nidulans afl R. In support of this hypothesis, we demonstrated that induced express ion of the A. flavus aflR gene in A. nidulans, under conditions that n ormally suppress ST gene expression, resulted in activation of genes i n the ST biosynthetic pathway. This result demonstrates that AflR func tion is conserved between Aspergillus spp. and that aflR expression is sufficient to activate genes in the ST pathway.