Genetic control of chromosome instability in Aspergillus nidulans as a mean for gene amplification in eukaryotic microorganisms

A simple method for the detection of recombinogenic substances in filamentous fungi

Several tests are available for detecting mutagenic and recombinogenic products in fungi. Since fungi are eukaryotic, these tests permit the detection of substances that produce chromosomal aberrations, or that are recombinogenic. We have developed a new method for testing substances that affect fungal stability using a duplication strain of Aspergillus nidulans and circular statistics for data analysis. The fungus was inoculated on the center of Petri dishes and the substance to be tested was applied to a defined area of the dish. Position of resulting sectors was measured by an angle and the data were analyzed by the Rayleigh test. Extensive testing with different compounds showed this method to be rapid and efficient for screening recombinogenic substances.

The penicillin gene cluster is amplified in tandem repeats linked by conserved hexanucleotide sequences

The penicillin biosynthetic genes (pcbAB, pcbC, penDE) of Penicillium chrysogenum AS-P-78 were located in a 106.5-kb DNA region that is amplified in tandem repeats (five or six copies) linked by conserved TTTACA sequences. The wild-type strains P. chrysogenum NRRL 1951 and Penicillium notatum ATCC 9478 (Fleming's isolate) contain a single copy of the 106.5-kb region. This region was bordered by the same TTTACA hexanucleotide found between tandem repeats in strain AS-P-78. A penicillin overproducer strain, P. chrysogenum E1, contains a large number of copies in tandem of a 57.9-kb DNA fragment, linked by the same hexanucleotide or its reverse complementary TGTAAA sequence. The deletion mutant P. chrysogenum npe10 showed a deletion of 57.9 kb that corresponds exactly to the DNA fragment that is amplified in E1. The conserved hexanucleotide sequence was reconstituted at the deletion site. The amplification has occurred within a single chromosome (chromosome I). The tandem reiteration and deletion appear to arise by mutation-induced site-specific recombination at the conserved hexanucleotide sequences.

Large amplification of a 35-kb DNA fragment carrying two penicillin biosynthetic genes in high penicillin producing strains of Penicillium chrysogenum

The isopenicillin N synthase (pcbC) and acyl-CoA:6-APA acyltransferase (penDE) genes of Penicillium chrysogenum were located in a 19.5-kb DNA fragment that had been previously cloned in phage vector EMBL3. This 19.5-kb DNA fragment was mapped with several endonucleases, and the pcbC and penDE genes were located by hybridization with probes corresponding to internal fragments of each gene. A low penicillin producing strain (P. chrysogenum Wis 54-1255) and two high producing strains (AS-P-78 and P2) showed hybridizing fragments of identical sizes in their chromosomes. Dot-blot hybridization of serial dilutions of the total DNA of the three strains showed that the intensity of all the hybridizing bands was much higher in strains AS-P-78 and P2 than in Wis 54-1255. Hybridization of total DNA digestions with probes corresponding to fragments which mapped upstream or downstream of the pcbC-penDE region revealed that a fragment of at least 35 kb DNA has been amplified 9 to 14 fold in the high penicillin producing strains. The amplified region did not include the previously cloned pyrG gene that encodes OMP-decarboxylase, an enzyme involved in pyrimidine biosynthesis.

Effect of the bncA gene on the instability of Aspergillus nidulans

The presence of a gene designatedbncAwhich produces binucleate and trinucleate conidia inA. nidulansalters the instability of disomics, diploids, and strains with chromosome duplication. In disomics, the genebncAincreases instability. In duplicate and diploid strains, thebncAgene reduces instability by acting as a partial stabilizer. In the strain with chromosome duplication, thebncAgene produces increased percentages of bi- and trinucleate conidia, a fact that may be interpreted to be due to the larger conidial volume of this strain or to the combined effect ofbncAand of the strain, which normally already exhibits a small amount of binucleate conidia.