Sequence variability in homologs of the aflatoxin pathway gene aflR distinguishes species in Aspergillus section Flavi.

Abstract

The Aspergillus parasiticus aflR gene, a gene that may be involved in the regulation of aflatoxin biosynthesis, encodes a putative zinc finger DNA-binding protein. PCR and sequencing were used to examine the presence of aflR homologs in other members of Aspergillus Section Flavi. The predicted amino acid sequences indicated that the same zinc finger domain, CTSCASSKVRCTKEKPACARCIERGLAC, was present in all of the Aspergillus sojae, Aspergillus flavus, and Aspergillus parasiticus isolates examined and in some of the Aspergillus oryzae isolates examined. Unique base substitutions and a specific base deletion were found in the 5' untranslated and zinc finger region; these differences provided distinct fingerprints. A. oryzae and A. flavus had the T-G-A-A-X-C fingerprint, whereas A. parasiticus and A sojae had the C-C-C-C-C-T fingerprint at the corresponding positions. Specific nucleotides at positions -90 (C or T) and -132 (G or A) further distinguished A. flavus from A. oryzae and A. parasiticus from A. sojae, respectively. A sojae ATCC 9362, which was previously designated A. oryzae NRRL 1988, was determined to be a A. sojae strain on the basis of the presence of the characteristic fingerprint, A-C-C-C-C-C-C-T. The DNAs of other members of Aspergillus Section Flavi, such as Aspergillus nomius and Aspergillus tamarii, and some isolates of A. oryzae appeared to exhibit low levels of similarity to the A. parasiticus aflR gene since low amounts of PCR products or no PCR products were obtained when DNAs from these strains were used.