TamA interacts with LeuB, the homologue of Saccharomyces cerevisiae Leu3p, to regulate gdhA expression in Aspergillus nidulans.

Previous studies have shown that expression of the gdhA gene, encoding NADP-linked glutamate dehydrogenase (NADP-GDH), in Aspergillus nidulans is regulated by the major nitrogen regulatory protein AreA and its co-activator TamA. We show here that loss of TamA function has a more severe effect on the levels of gdhA expression than loss of AreA function. Using TamA as the bait in a yeast two-hybrid screen, we have identified a second protein that interacts with TamA. Sequencing analysis and functional studies have shown that this protein, designated LeuB, is a transcriptional activator with similar function to the homologous Leu3p of Saccharomyces cerevisiae. Inactivation of leuB revealed that this gene is involved in the regulation of gdhA, and an areA; leuB double mutant was shown to have similar NADP-GDH levels to a tamA single mutant. The requirement for TamA function to promote gdhA expression is likely to be due to its dual interaction with AreA and LeuB.