CHARACTERIZATION OF AFLJ, A GENE REQUIRED FOR CONVERSION OF PATHWAY INTERMEDIATES TO AFLATOXIN

The genes encoding the aflatoxin biosynthetic pathway enzymes have bee n localized as a cluster to a 75 kb DNA fragment. The enzymatic functi ons of the products of most of the genes in the cluster are known, but there are a few genes that have not yet been characterized. We report here the characterization of one of these genes, a gene designated af lJ. This gene resides in the cluster adjacent to the pathway regulator y gene, aflR, and the two genes are divergently transcribed. Disruptio n of aflJ in Aspergillus flavus results in a failure to produce aflato xins and a failure to convert exogenously added pathway intermediates norsolorinic acid, sterigmatocystin, and O-methylsterigmatocystin to a flatoxin, The disrupted strain do es, however, accumulate pksA, nor-1, ver-1, and omtA transcripts under conditions conducive to aflatoxin b iosynthesis, Therefore, disruption of aflJ does not affect transcripti on of these genes, and aflJ does not appear to have a regulatory funct ion similar to that of aflR. Sequence analysis of aflJ and its putativ e peptide, AflJ, did not reveal any enzymatic domains or significant s imilarities to proteins of known function. The putative peptide does c ontain three regions predicted to be membrane-spanning domains and a m icrobodies C-terminal targeting signal.