Sequence and regulation of the uapA gene encoding a uric acid-xanthine permease in the fungus Aspergillus nidulans

Abstract

The nucleotide sequence of the uapA gene, coding for the uric acid-xanthine permease of Aspergillus nidulans, has been determined. The predicted uapA gene product comprises 595 amino acids (M(r) 63,365); it is a highly hydrophobic protein with 12-14 putative transmembrane segments and shows no striking similarity to any other membrane protein of either prokaryotes or eukaryotes, except for a short highly hydrophobic amino acid sequence conserved in a number of different permeases. The presence of an acidic, amphipathic region overlapping with the last hydrophobic segment of UAPA could also be of interest. The results presented suggest that the UAPA permease represents a new type of membrane protein, not described previously. The transcription of uapA is inducible by 2-thiouric acid, and it is highly repressible by ammonium. It is almost absolutely dependent on the presence of functional uaY and areA regulatory gene products. A specific mutation in the GATA binding zinc finger of the AREA protein nearly abolishes uapA transcription. The uap100 cis-acting, up-promoter, constitutive mutation is a duplication that comprises two GATA sites and suppresses weakly the AREA zinc finger mutation but does not alleviate the need for functional UAY and AREA proteins.