INCREASED EXPRESSION OF ASPERGILLUS-PARASITICUS AFLR, ENCODING A SEQUENCE-SPECIFIC DNA-BINDING PROTEIN, RELIEVES NITRATE INHIBITION OF AFLATOXIN BIOSYNTHESIS

The aflR gene from Aspergillus parasiticus and Aspergillus flavus may be involved in the regulation of ah aflatoxin biosynthesis. The aflR g ene product, AFLR, possesses a GAL4-type binuclear zinc finger DNA-bin ding domain. A transformant, SU1-N3(pHSP), containing an additional co py of aflR, showed increased transcription of aflR and the aflatoxin p athway structural genes, nor-1, ver-1, and omt-1, when cells were grow n in nitrate medium, which normally suppresses aflatoxin production. E lectrophoretic mobility shift assays showed that the recombinant prote in containing the DNA-binding domain, AFLR1, bound specifically to the palindromic sequence, TTAGGCCTAA, 120 bp upstream of the AFLR transla tion start site. Expression of aflR thus appears to be autoregulated. Increased expression of aflatoxin biosynthetic genes in the transforma nt might result from an elevated basal level of AFLR, allowing it to o vercome nitrate inhibition and to bind to the aflR promotor region, th ereby initiating aflatoxin biosynthesis. Results further suggest that aflR is involved in the regulation of multiple parts of the aflatoxin biosynthetic pathway.