A mutation defective in the xanthine alternative pathway of Aspergillus nidulans: its use to investigate the specificity of uaY mediated induction.

In Aspergillus nidulans uric acid can be produced from xanthine via purine hydroxylase I (xanthine dehydrogenase) or via the xanthine alternative pathway (Darlington and Scazzocchio, Biochem. Biophys. Acta, 166, 569--571; 1968). A mutation defective in the xanthine alternative pathway of Aspergillus nidulans is described. By combining this mutation with hxB-20 which results in complete loss of purine hydroxylase I and II activities, but which conserves cross-reacting material, it is possible to block completely uric acid production and thus investigate which are the effective in vivo inducers of three enzymes under the control of the positive regulatory gene uaY: adenine deaminase, purine hydroxylase I (measured as cross-reacting material) and urate oxidase. It is concluded that uric acid is the only effective physiological inducer, while its 2 and 8 thio-analogues serve as gratuitous inducers.