Isolation and characterization of the urease gene (URE) from the pathogenic fungus Coccidioides immitis

The urease (URE)-encoding gene from Coccidioides immitis (Ci), a respiratory fungal pathogen of humans, was cloned, sequenced, chromosome-mapped and expressed. Both the genomic and cDNA sequences are reported. The transcription start point and poly(A)-addition site were confirmed. The URE gene contains eight introns and a 2517-bp ORF that translates a 839-amino-acid (aa) protein of 91.5 kDa and pI of 5.5, as deduced by computer analysis of the nucleotide sequence. The translated protein revealed eight putative N-glycosylation sites. The deduced URE showed comparable levels of homology to reported URE of the jack bean plant (Canavalia ensiformis; 71.8%) and URE of several genera of bacteria (Bp, 71.7%; Hp, 68.3%; Ka, 71.6%; Pm, 71.9%). The URE gene was mapped to chromosome III of Ci and was shown to be a single copy gene by Southern hybridization. Expression of a 1687-bp fragment of the URE gene in E. coli resulted in the production of a 63-kDa recombinant protein that was recognized in an immunoblot by antiserum raised against the Ka URE homolog. This is the first report of a fungal URE gene.