Mutations in the basic loop of the Zn binuclear cluster of the UaY transcriptional activator suppress mutations in the dimerisation domain

Regulation of nutrient utilization in filamentous fungi

Organisms must accurately sense and respond to nutrients to survive. In filamentous fungi, accurate nutrient sensing is important in the establishment of fungal colonies and in continued, rapid growth for the exploitation of environmental resources. To ensure efficient nutrient utilization, fungi have evolved a combination of activating and repressing genetic networks to tightly regulate metabolic pathways and distinguish between preferred nutrients, which require minimal energy and resources to utilize, and nonpreferred nutrients, which have more energy-intensive catabolic requirements. Genes necessary for the utilization of nonpreferred carbon sources are activated by transcription factors that respond to the presence of the specific nutrient and repressed by transcription factors that respond to the presence of preferred carbohydrates. Utilization of nonpreferred nitrogen sources generally requires two transcription factors. Pathway-specific transcription factors respond to the presence of a specific nonpreferred nitrogen source, while another transcription factor activates genes in the absence of preferred nitrogen sources. In this review, we discuss the roles of transcription factors and upstream regulatory genes that respond to preferred and nonpreferred carbon and nitrogen sources and their roles in regulating carbon and nitrogen catabolism. KEY POINTS: • Interplay of activating and repressing transcriptional networks regulates catabolism. • Nutrient-specific activating transcriptional pathways provide metabolic specificity. • Repressing regulatory systems differentiate nutrients in mixed nutrient environments.

A novel enzymatic approach in the production of food with low purine content using Arxula adeninivorans endogenous and recombinant purine degradative enzymes

The purine degradation pathway in humans ends with uric acid, which has low water solubility. When the production of uric acid is increased either by elevated purine intake or by impaired kidney function, uric acid will accumulate in the blood (hyperuricemia). This increases the risk of gout, a disease described in humans for at least 1000 years. Many lower organisms, such as the yeast Arxula adeninivorans, possess the enzyme, urate oxidase that converts uric acid to 5-hydroxyisourate, thus preventing uric acid accumulation. We have examined the complete purine degradation pathway in A. adeninivorans and analyzed enzymes involved. Recombinant adenine deaminase, guanine deaminase, urate oxidase and endogenous xanthine oxidoreductase have been investigated as potential additives to degrade purines in the food. Here, we review the current model of the purine degradation pathway of A. adeninivorans and present an overview of proposed enzyme system with perspectives for its further development.

Characterization of the mutagenic spectrum of 4-nitroquinoline 1-oxide (4-NQO) in Aspergillus nidulans by whole genome sequencing

4-Nitroquinoline 1-oxide (4-NQO) is a highly carcinogenic chemical that induces mutations in bacteria, fungi, and animals through the formation of bulky purine adducts. 4-NQO has been used as a mutagen for genetic screens and in both the study of DNA damage and DNA repair. In the model eukaryote Aspergillus nidulans, 4-NQO-based genetic screens have been used to study diverse processes, including gene regulation, mitosis, metabolism, organelle transport, and septation. Early work during the 1970s using bacterial and yeast mutation tester strains concluded that 4-NQO was a guanine-specific mutagen. However, these strains were limited in their ability to determine full mutagenic potential, as they could not identify mutations at multiple sites, unlinked suppressor mutations, or G:C to C:G transversions. We have now used a whole genome resequencing approach with mutant strains generated from two independent genetic screens to determine the full mutagenic spectrum of 4-NQO in A. nidulans. Analysis of 3994 mutations from 38 mutant strains reveals that 4-NQO induces substitutions in both guanine and adenine residues, although with a 19-fold preference for guanine. We found no association between mutation load and mutagen dose and observed no sequence bias in the residues flanking the mutated purine base. The mutations were distributed randomly throughout most of the genome. Our data provide new evidence that 4-NQO can potentially target all base pairs. Furthermore, we predict that current practices for 4-NQO-induced mutagenesis are sufficient to reach gene saturation for genetic screens with feasible identification of causative mutations via whole genome resequencing.