Abstract
In this paper we characterize genetically a positive eukaryotic regulatory gene: the uaY gene of the ascomycete Aspergillus nidulans. Several steps in the uptake and degradation of purines are under the control of the uaY gene (summarized in Scazzocchio and Gorton 1977). In the present paper 12 uaY- mutations are characterized with respect to their inducibility for adenine deaminase, xanthine dehydrogenase (purine hydroxylase I) and urate oxidase and by the absence of the uric acid-xanthine permease scored in vivo by resistance to 2-thiouric acid. While 10 mutations are uniformly unleaky, two others are almost wild type for the induction of urate oxidase. A fine structure map of the uaY gene shows that the two "leaky" mutations are not clustered. The fine structure mapping unambiguously positions six uaY alleles and provides preliminary but interesting trends regarding the pattern of gene conversion in the uaY gene. The enzyme levels in all uaY-/uaY+ heterozygous diploids are intermediate between the corresponding uaY-/uaY- and uaY+/uaY+ homozygous diploids, suggesting that one functional copy of the uaY gene is able to mediate the complete induction of only one set of structural genes. No complementation was found between any two uaY- alleles. This establishes that the mutations showing either of the phenotypes are alleles in the same gene; it fails to provide evidence for intracistronic complementation. A mutation, oxpA5, causes resistance to the xanthine analogue oxypurinol (4, 6-dihydroxypyrazolo-(3, 4-d)-pyrimidine) and partial constitutivity of adenine deaminase, xanthine dehydrogenase (purine hydroxylase I) and urate oxidase. The constitutive phenotype is suppressed by mutations blocking the synthesis of intracellular inducers. The mutation is recessive and complements fully with the 11 uaY- mutations tested. It maps to the left of all 12 uaY mutations to which it has been crossed. The data indicate that both the resistance and constitutivity arise from one mutational event in a gene, oxpA, different from uaY and possibly adjacent to it. We propose that the oxpA gene codes for a protein involved in limiting the flow of inducers into the cell nucleus. Thus oxpA and uaY constitute a regulatory gene cluster, indicating that uaY is the regulatory gene.
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Selected References
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- Alderson T., Hartley M. J. Specificity for spontaneous and induced forward mutation at several gene loci in Aspergillus nidulans. Mutat Res. 1969 Sep-Oct;8(2):255–264. doi: 10.1016/0027-5107(69)90005-0. [DOI] [PubMed] [Google Scholar]
- Darlington A. J., Scazzocchio C., Pateman J. A. Biochemical and genetical studies of purine breakdown in Aspergillus. Nature. 1965 May 8;206(984):599–600. doi: 10.1038/206599a0. [DOI] [PubMed] [Google Scholar]
- Elorza M. V., Arst H. N., Jr Sorbose resistant mutants of Aspergillus nidulans. Mol Gen Genet. 1971;111(2):185–193. doi: 10.1007/BF00267792. [DOI] [PubMed] [Google Scholar]
- Graham R. C., Jr, Karnovsky M. J. The histochemical demonstration of uricase activity. J Histochem Cytochem. 1965 Jul-Aug;13(6):448–453. doi: 10.1177/13.6.448. [DOI] [PubMed] [Google Scholar]
- Gunatilleke I. A., Arst H. N., Jr, Scazzocchio C. Three genes determine the carboxin sensitivity of mitochondrial succinate oxidation in aspergillus nidulans. Genet Res. 1975 Dec;26(3):297–305. doi: 10.1017/s0016672300016098. [DOI] [PubMed] [Google Scholar]
- Riggs A. D., Bourgeois S. On the assay, isolation and characterization of the lac repressor. J Mol Biol. 1968 Jul 14;34(2):361–364. doi: 10.1016/0022-2836(68)90260-x. [DOI] [PubMed] [Google Scholar]
- Scazzocchio C., Holl F. B., Foguelman A. I. The genetic control of molybdoflavoproteins in Aspergillus nidulans. Allopurinol-resistant mutants constitutive for xanthine-dehydrogenase. Eur J Biochem. 1973 Jul 16;36(2):428–445. doi: 10.1111/j.1432-1033.1973.tb02928.x. [DOI] [PubMed] [Google Scholar]
- Sealy-Lewis H. M., Scazzocchio C., Lee S. A mutation defective in the xanthine alternative pathway of Aspergillus nidulans: its use to investigate the specificity of uaY mediated induction. Mol Gen Genet. 1978 Sep 8;164(3):303–308. doi: 10.1007/BF00333161. [DOI] [PubMed] [Google Scholar]