Genetic and Molecular Characterization of a Gene Encoding a Wide Specificity Purine Permease of Aspergillus nidulans Reveals a Novel Family of Transporters Conserved in Prokaryotes and Eukaryotes

Abstract

In Aspergillus nidulans, loss-of-function mutations in the uapA and azgA genes, encoding the major uric acid-xanthine and hypoxanthine-adenine-guanine permeases, respectively, result in impaired utilization of these purines as sole nitrogen sources. The residual growth of the mutant strains is due to the activity of a broad specificity purine permease. We have identified uapC, the gene coding for this third permease through the isolation of both gain-of-function and loss-of-function mutations. Uptake studies with wild-type and mutant strains confirmed the genetic analysis and showed that the UapC protein contributes 30% and 8-10% to uric acid and hypoxanthine transport rates, respectively. The uapC gene was cloned, its expression studied, its sequence and transcript map established, and the sequence of its putative product analyzed. uapC message accumulation is: (i) weakly induced by 2-thiouric acid; (ii) repressed by ammonium; (iii) dependent on functional uaY and areA regulatory gene products (mediating uric acid induction and nitrogen metabolite repression, respectively); (iv) increased by uapC gain-of-function mutations which specifically, but partially, suppress a leucine to valine mutation in the zinc finger of the protein coded by the areA gene. The putative uapC gene product is a highly hydrophobic protein of 580 amino acids (M(r) = 61,251) including 12-14 putative transmembrane segments. The UapC protein is highly similar (58% identity) to the UapA permease and significantly similar (23-34% identity) to a number of bacterial transporters. Comparisons of the sequences and hydropathy profiles of members of this novel family of transporters yield insights into their structure, functionally important residues, and possible evolutionary relationships.

Complete Nucleotide Sequence and Organization of the Atrazine Catabolic Plasmid pADP-1 from Pseudomonas sp . Strain ADP

“…These ORFs were classified as transporters based on results obtained from domain searches done using Pfam. ORF46 (46883 to 48223) showed a significant match to a xanthine/ uracil permease family of proteins, having many residues conserved in the signature sequence of this family of proteins (1,19). In addition, hydrophobicity plots of ORF46 predicted 12 transmembrane domains, a characteristic that is commonly observed in the xanthine/uracil permease family of proteins (1,19).…”

“…ORF46 (46883 to 48223) showed a significant match to a xanthine/ uracil permease family of proteins, having many residues conserved in the signature sequence of this family of proteins (1,19). In addition, hydrophobicity plots of ORF46 predicted 12 transmembrane domains, a characteristic that is commonly observed in the xanthine/uracil permease family of proteins (1,19). Similarly, hydrophobicity plots of ORF69 (67797 to 68942) showed 12 membrane-spanning domains, and BLAST and Pfam searches showed predicted homology to a variety of transporters.…”

The Clostridium perfringens enterotoxin gene is on a transposable element in type A human food poisoning strains

“…New entries in the databases, along with corrections in the sequence, gave identities to the two unidentified ORFs and a better total homology to IS200 for ORF3. ORFl has high homology to the purine permease gene uapC in Aspergillus nidulans (Diallinas et al, 1995). This is a housekeeping gene, and has a stable position on the chromosome of the strains that have been examined, ORF2 has been registered, according to convention, as IS1470 (Lederberg, 1987).…”

AtAzg1 and AtAzg2 comprise a novel family of purine transporters in Arabidopsis

“…Nucleobase-ascorbate transporters (NATs) are ubiquitous and transport oxidized purines, xanthine, hypoxanthine and uric acid, uracil, or ascorbate [3][4][5][6]. None of the 12 identified Arabidopsis NAT loci are yet functionally characterized.…”