The oxpA5 mutation of Aspergillus nidulans is an allele of adB, the gene encoding adenylosuccinate synthetase

Abstract

The oxpA5 mutation in Aspergillus nidulans results in a pleiotropic phenotype, including resistance to oxypurinol and partial constitutivity of the enzymes of purine catabolism. Here we show that the oxpA5 mutation is an allele of adB, the gene encoding adenylosuccinate synthetase (ASS). Cloning, sequencing and characterisation of the adB gene are reported in this paper. In vivo complementation tests indicate that the oxpA5 mutation is a partial loss-of-function mutation, and altered kinetic parameters of the ASS could account for the pleiotropic phenotype of the oxpA5 mutant. The transcriptional regulation of adB presents some interesting features, including increased gene expression in the presence of ammonium and of AMP, the final product of purine biosynthesis. The adB gene is located adjacent to helA, a newly identified gene coding for a putative RNA helicase.

Phenotypes of Mutations in the 5′-UTR of a Limiting Transcription Factor in Aspergillus nidulans Can Be Accounted For by Translational Inhibition and Leaky Scanning

“…Note: the suaC109 uaY1 strain is in an oxpA5 genetic background. In the presence of this partial loss of function of the adB gene (encoding adenylosuccinate synthetase), the expression of the UaY-dependent genes is slightly enhanced (Ribard et al 2001). scription of hxA, uaZ, and uapA is partially restored in both 12r122 and 12r128 strains.…”

“…Again, the whole inserts of these plasmids were sequenced (Fasteris, Switzerland), using the T3 primer, to ensure that no mutation was introduced by the PCR process. To expand the size of the insert on both sides of the XhoI-ClaI fragment, two successive steps were carried out: First, a 2836-bp ApaI-XhoI fragment (À2611 to À225) from plasmids bAN783 (Ribard et al 2001) was inserted in all the six bAN772-X plasmids, creating the bAN755-X plasmids (see supplemental material). Second, a 1403-bp ClaI-EcoRI fragment (1203 to 11606) from plasmids bAN753 (Suárez et al 1991b) was inserted in all the six bAN755-X plasmids, creating the final bAN756-X plasmids (see supplemental Table 2).…”

The nadA gene of Aspergillus nidulans, encoding adenine deaminase, is subject to a unique regulatory pattern

“…Purine metabolism includes three related pathways: de novo biosynthesis, the purine nucleotide cycle (or purine salvage pathway) and purine catabolism. A. nidulans is able to synthesise purines de novo and mutants blocked before and after IMP synthesis are available (Foley et al, 1965;Ribard et al, 2001, see http://www.gla.ac.uk/Acad/ IBLS/molgen/aspergillus/locia. html2001 for gene/enzyme relationships).…”

Nitrogen Regulation in Mycelial Fungi

“…The loci adB, which encodes adenylosuccinate synthetase (Ribard et al 2001), and nadA, which encodes adenine deaminase, both show increased transcription in the presence of ammonium. It has been shown that nadA is negatively regulated by areA (c. Ribard, C. Scazzocchio and N. Oestreicher, pers.…”