Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 14, 2003
Publication Date: March 18, 2003
Citation: Chang, P. 2003. Aspergillus parasiticus aflj interacts with aflr and regulates transcription of aflatoxin biosynthetic pathway genes [abstract]. XXII Fungal Genetics Conference, March 13-18, 2003, Pacific Grove, Californa. p. 33. Technical Abstract: The Aspergillus parasiticus aflJ gene, located in the aflatoxin biosynthetic gene cluster and divergently transcribed from the aflatoxin pathway regulatory gene aflR, encodes a 438-amino acid protein. Disruption of aflJ resulted in non-pigmented mutants that lost the ability to synthesize aflatoxin intermediates. Transcript profiling by real time RT-PCR indicated that a lack of the aflJ transcript in the aflJ knockout mutants significantly decreased the transcript levels of the genes of the early (pksA and nor1), middle (ver1) and later (omtA) steps of aflatoxin biosynthetic pathway, respectively, and the reduction ranged from 5 to 20-fold. Deletion of aflJ, however, did not correlate with changes in the aflR transcript level and vice versa. Two-hybrid assays showed that AFLJ did not interact with aflatoxin biosynthetic enzymes, including NOR1, VER1, OMTA and ORDA. But AFLJ interacted with full-length AFLR, and the DNA-binding domain of AFLR was not essential for the interaction. Simultaneous substitutions of Arg427, Arg429, and Arg431 at the carboxyl terminus of AFLR with Leu abolished its interaction with AFLJ. Substitution of Asp436, previously shown to be crucial for AFLR's activation activity, with His had little effect on the interaction. Deletions in most regions of AFLJ appeared to destroy its function despite the fact that random amino acid substitution(s) at its carboxyl terminus did not drastically affect its capacity to interact with AFLR. The results show that aflJ is involved in the expression of aflatoxin structural genes and support the hypothesis that aflJ is a coactivator gene.