MOLECULAR CHARACTERIZATION OF AFLR, A REGULATORY LOCUS FOR AFLATOXIN BIOSYNTHESIS

Aflatoxins belong to a family of decaketides that are produced as seco ndary metabolites by Aspergillus flavus and A. parasiticus. The aflato xin biosynthetic pathway involves several enzymatic steps that appear to be regulated by the afl2 gene in A. flavus and the apa2 gene in A. parasiticus. Several lines of evidence indicate that these two genes a re homologous. The DNA sequences of the two genes are highly similar, they both are involved in the regulation of aflatoxin biosynthesis, an d apa2 can complement the afl2 mutation in A. flavus. Because of these similarities, we propose that these two genes are homologs, and becau se of the ability of these genes to regulate aflatoxin biosynthesis, w e suggest that they be designated aflR. We report here the further cha racterization of aflR fi-om A. flavus and show that aflR codes for a 2 ,078-bp transcript with an open reading frame of 1,311 nucleotides tha t codes for 437 amino acids and a putative protein of 46,679 daltons. Analysis of the predicted amino acid sequence indicated that the polyp eptide contains a zinc cluster motif between amino acid positions 29 a nd 56. This region contains the consensus sequence Cys-Xaa2-Cys-Xaa6-C ys-Xaa6-Cys-Xaa2-Cys-Xaa6-Cys. This motif has been found in several fu ngal transcriptional regulatory proteins. DNA hybridization of the afl R gene with genomic digests of seven polyketide-producing fungi reveal ed similar sequences in three other species related to A. flavus: A. p arasiticus, A. oryzae, and A. sojae. Finally, we present evidence for an antisense transcript (aflRas) derived from the opposite strand of a flR, suggesting that the aflR locus involves some form of antisense re gulation.