The formamidase gene of Aspergillus nidulans: Regulation by nitrogen metabolite repression and transcriptional interference by an overlapping upstream gene

The ability to utilize formamide as a sole nitrogen source has been found i n numerous fungi. We have cloned the fmdS gene encoding a formamidase from Aspergillus nidulans and found that it belongs to a highly conserved family of proteins separate from the major amidase families. The expression of fm dS is primarily regulated via AreA-mediated nitrogen metabolite repression and does not require the addition of exogenous inducer. Consistent with thi s, deletion analysis of the 5' region of fmdS has confirmed the presence of multiple AreA-binding sites containing a characteristic core GATA sequence . Under carbon starvation conditions the response to nitrogen starvation is eliminated, indicating that the lack of a carbon soul co may result in ina ctivation of ArcA. Sequence analysis and isolation of cDNAs show that a gen e of 5' or fmdS with its transcript overlapping the fmdS coding region. Dis ruption unknown function lies directly 5' of the 5' gene and analysis of th e effects of overexpression of this gene on fmdS expression has shown that expression of this upstream gene interferes with fmdS transcription, result ing in a strong dependence on AreA activation for expression. Therefore the relative position of these two genes is essential fur normal regulation of fmdS.