The multiply-regulated gabA gene encoding the GABA permease of Aspergillus nidulans: a score of exons.

We describe the cloning, sequence and expression of gabA, encoding the gamma-amino-n-butyrate (GABA) permease of the fungus Aspergillus nidulans. Sequence changes were determined for three up-promoter (gabI ) and six gabA loss-of-function mutations. The predicted protein contains 517 residues and shows 30.3% overall identity with a putative GABA permease of Arabidopsis thaliana, 29.6% identity with the yeast choline transporter and 23.4% identity with the yeast UGA4 GABA permease. Structural predictions favour 11-12 transmembrane domains. Comparison of the genomic and cDNA sequences shows the presence of 19 introns, an unusually large number of introns for, we believe, any fungal gene. In agreement with the wealth of genetic data available, transcript level analyses demonstrate that gabA is subject to carbon catabolite and nitrogen metabolite repression, omega-amino acid induction and regulation in response to ambient pH (being acid-expressed). In agreement with this, we report consensus binding sites 5' to the coding region, six each for CreA and AREA and one for PacC, the transcription factors mediating carbon catabolite and nitrogen metabolite repression and response to ambient pH respectively.