Previous studies found that the protein AflJ is required for aflatoxin biosynthesis. AflJ is predicted to have at least three membrane spanning domains and a C-terminal microbody targeting signal. Interaction between AflR and AflJ was shown to be necessary for aflatoxin biosynthesis. In knockout transformants of aflJ in A. parasiticus or A. flavus, transcripts of biosynthesis genes were detected suggesting that AflJ acts post- transcriptionally. W e now report, based on a yeast two-hybrid assay, that AflJ interacts with fungal homologs of subunits 5 (CsnE) and 6 (CsnF) of the COP9 signalosome complex, as well as a putative NEDD8 activating enzyme (UbaC). The latter homolog is predicted to activate ubiquitination while the former may affect ubiquitin-mediated protein degradation. The association of AflJ with components of the protein degradation pathway suggests a plausible mechanism for its action consistent with previously reported observations. AflJ may specifically prevent degradation of enzymes critical to aflatoxin biosynthesis. Thus, in aflR knockout transformants, the transcripts of aflatoxin biosynthesis genes are still made but some of the proteins may be swiftly degraded, thereby preventing buildup of sufficient enzyme pools to carry out the necessary biosynthetic steps.
Full conference title:
6th International Aspergillus Meeting
- Asperfest 6 (2009)