Elsevier, Fungal Genetics and Biology, (69), p. 96-108, 2014
DOI: 10.1016/j.fgb.2014.06.005
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The purine utilisation pathway has been thoroughly characterised in Aspergillus nidulans. We establish here the subcellular distribution of seven key intracellular enzymes, xanthine dehydrogenase (HxA), urate oxidase (UaZ), 5-hydroxy-isourate hydrolase (UaX), 2-oxo-4-hydroxy-4-carboxy ureido imidazoline carboxylase (UaW), allantoinase (AlX), allantoicase (AaX), ureidoglycolase lyase (UglA), and the fungal-specific α-ketoglutarate Fe(II)-dependent dioxygenase (XanA). HxA, AlX, AaX, UaW and XanA are cytosolic, while UaZ, UaX and UglA are peroxisomal. Peroxisomal localization was confirmed by using appropriate pex mutants. The pathway is largely, but not completely conserved in the Eurotiomycetes, noticeably in some species AaX is substituted by an alternative enzyme of probable bacterial origin. UaZ and the urate-xanthine UapA and UapC transporters, are also localised in specific cells of the conidiophore. We show that metabolic accumulation of uric acid occurring in uaZ null mutations is associated with an increased frequency of appearance of morphologically distinct colony sectors, diminished conidiospore production, UV resistance and an altered response to oxidation stress, which may provide a rationale for the conidiophore-specific localisation. The pathway-specific transcription factor UaY is localized in both the cytoplasm and nuclei under non-inducing conditions, but it rapidly accumulates exclusively to the nuclei upon induction by uric acid.