Isolation and characterisation of nuv11, a mutation affecting meiotic and mitotic recombination in Aspergillus nidulans

Recombinagenic effect of cryptolepine in uvsH+//uvsH+ and uvsH//uvsH diploid strains of Aspergillus nidulans

Recombinagenic potential of the alkaloid cryptolepine was evaluated in two diploid strains of Aspergillus nidulans--a wild type strain (uvsH+//uvsH+) and a DNA-repair-deficient one (uvsH//uvsH). Treatment of both strains with cryptolepine failed to alter colony growth in culture; its recombinagenic potential was determined by the homozygotization index (in which events of mitotic exchange may cause expression of genes previously masked by the dominant allele). Mitotic crossing-overs were induced by 7 and 14 mg/L doses of cryptolepine in both diploid A. nidulans strains.

nuvA, an Aspergillus nidulans gene involved in DNA repair and recombination, is a homologue of Saccharomyces cerevisiae RAD18 and Neurospora crassa uvs-2

A 40 kb genomic clone and 2.3 kb EcoRI subclone that rescued the DNA repair and recombination defects of the Aspergillus nidulans nuvA11 mutant were isolated and the subclone sequenced. The subclone hybridized to a cosmid in a chromosome-specific library confirming the assignment of nuvA to linkage group IV and indicating its closeness to bimD. Amplification by PCR clarified the relative positions of nuvA and bimD. A region identified within the subclone, encoding a C3HC4 zinc finger motif, was used as a probe to retrieve a cDNA clone. Sequencing of this clone showed that the nuvA gene has an ORF of 1329 bp with two introns of 51 bp and 60 bp. Expression of nuvA appears to be extremely low. The putative NUVA polypeptide has two zinc finger motifs, a molecular mass of 48906 Da and has 39% identity with the Neurospora crassa uvs-2 and 25% identity with the Saccharomyces cerevisiae RAD18 translation products. Although mutations in nuvA, uvs-2 and RAD18 produce similar phenotypes, only the nuvA11 mutation affects meiotic recombination. A role for nuvA in both DNA repair and genetic recombination is proposed.

The isolation of mutagen-sensitive nuv mutants of Aspergillus nidulans and their effects on mitotic recombination

More than 200 mutants of Aspergillus nidulans were isolated as hypersensitive to the monofunctional alkylating agent MNNG and/or UV-irradiation (designated nuv mutants). Of these, 23 were selected for further characterization. All were markedly hypersensitive to both MNNG and the quasi-UV-mimetic mutagen 4-NQO. The hypersensitive phenotype of each mutant was shown to result from mutation of a single gene. The nuv mutants exhibited a diverse range of growth responses on solid media containing various concentrations of MNNG or 4-NQO. This suggested that they represented many nonallelic mutations. Analysis to determine the dominance/recessiveness of the nuv mutations with respect to hypersensitivity revealed that most were fully recessive, although several appeared to be semidominant. A novel system to assay homologous mitotic recombination using simple plating tests was developed. The system was exploited to determine the effects of the nuv mutations on mitotic recombination. Of the 23 mutations tested, 10 caused a hypo-recombination phenotype and three a hyper-recombination phenotype, while 10 appeared to have no effect on recombination. The hypo-rec effect of one of the mutations, nuv-117, appeared to be semidominant. Transcomplementation analysis between seven of the nuv mutations defined at least six nonallelic loci.