Sequence, regulation, and mutational analysis of the gene encoding urate oxidase in Aspergillus nidulans

The uaZ gene of Aspergillus nidulans codes for a protein of 301 amino acids. The open reading frame is interrupted by two introns. A comparison with the open reading frames of 10 other urate oxidases reveals a number of scattered universally conserved residues and four clusters of high similarity. Two of these are of unknown function, and the other two are the putative sites for copper binding and the signal sequence for peroxisomal entry, respectively. This comparison also reveals that there are at 16 positions at which introns can be found in the gene coding for this enzyme in different species. The sequence of a number of mutations confirms the importance for enzyme activity of the carboxyl terminus of the protein. The most amino-terminal mutation (an ochre codon) results also in strikingly diminished steady-state levels of message. This agrees with results from other systems, suggesting that untranslated mRNA is preferentially degraded in eukaryotic cells. Northern blots show that specific induction, mediated by the UAY protein, and nitrogen metabolite repression, mediated by the AREA GATA factor, affect the steady-state levels of uaZ mRNA and thus act most probably at the level of transcription.