Transcription coactivator involved in regulation of the aflatoxin biosynthesis gene cluster with aflR (PubMed:15006741, PubMed:11913765, PubMed:12655397, PubMed:15054098, PubMed:23605486). The ratio of the expression data between aflS:aflR plays a crucial role in the regulation of aflatoxins production (PubMed:23605486). A high ratio, produced at a range between 17 and 30 degrees Celsius, corresponds with the production profile of aflatoxin G1 biosynthesis (PubMed:23605486). A low ratio, produced over 30 degrees Celsius, is related to aflatoxin B1 biosynthesis (PubMed:23605486). AflJ may act in aflR transport to or from the nucleus, thus controlling the availability of aflR for transcriptional activation of aflatoxin biosynthesis cluster genes (PubMed:23342682). AflJ may also assist in directing endosomes to the cytoplasmic membrane for aflatoxin export (PubMed:23342682). Interacts with aflR (PubMed:12655397, PubMed:15054098, PubMed:23342682). Expression is positively regulated by the developmental and secondary metabolism regulator veA (PubMed:15294809). Expression is repressed during Streptomyces-Aspergillus interactions (PubMed:25741015). Leads to significant decrease in the transcript levels of the genes for early (aflC and aflD), middle (aflM) and later (aflP) steps in the aflatoxin biosynthetic pathway (PubMed:12655397).