G. Morpurgo

Non-disjunction and crossing-over induced by pharmaceutical drugs in Aspergillus nidulans

Summary A system has been developed to test rapidly, with diploids of Aspergillus nidulans , the non-disjunction and crossing-over induced by drugs. The test permits a semiquantitation of the induced damage. 110 pharmaceutical specialities were tested. 13 of them strongly increased the incidence of somatic segregation. The spontaneous rate was approximately 1 · 10 -5 of non-disjunction. The drugs that were mutagenic belong to the following classes. (1) Quinolines—4 specialities containing quinolines of various types were tested. All increased the incidence of non-disjunction up to 36% of the plated conidia. (2) Sulfa drugs—6 were tested and all but 3 induced crossing-over. Maximal incidence was 45% of the plated conidia. (3) Benzodiazepines—8 were tested. Only one significantly increases non-disjunction. The frequency was 5%. (4) Pyrazolidines—9 were tested of which two induced non-disjunction. The frequency was 10%. (5) Various—chemicals of widely different composition were also mutagenic. These were: Entobex 15%, Mucoxin 11%, Tanderil 10%, Nitrofurin (nitrofurantoin) 12%, Lipopill (phentermine) 14%, Esidrex 96%.

Mutagenic and recombinogenic action of pesticides in Aspergillus nidulans

Thirteen pesticides, aminotriazole, benomyl, captafol, captan, dalapon-Na, dichlorvos, dinobuton, dodine, ioxynil, mecoprop, neburon, picloram and tordon were tested for ability to induce (1) point mutations to 8-azaguanine resistance, (2) mitotic crossing-over, and (3) mitotic non-disjunction and haploidization in Aspergillus nidulans. Tests were performed at three different pHs, i.e. 4.5, 7, 8.2. Three of the pesticides, captan , captafol and dichlorvos induced point mutations; dichlorvos also induced a high frequency of mitotic crossing-over and non-disjunction; benomyl induced a very high frequency of non-disjunction whereas aminotriazole induced weakly both types of somatic segregation.

Analysis of induced mutations in Aspergillus nidulans. I. UV- and HNO2-induced mutations.

Abstract A method is described that permits the selective detection of forward and back mutations for a single cistron in Aspergillus nidulans . The method also permits an easy phenotypic distinction among true back mutants and suppressor mutations. The rate of spontaneous, UV- and HNO 2 -induced retromutations has been studied in 15 UV- and 14 HNO 2 -induced mutants. Most of the UV-induced mutants can be interpreted as due to a base substitution while HNO 2 -induced mutants must be due to a different mechanism. Two mutants of this group present a rate of spontaneous retromutation 20–40 times higher than the rate of forward mutation in the whole cistron. The spontaneous rate of retromutation is not modified by treatment with five reference mutagens.

Mitotic intragenic recombination as a consequence of heteroduplex formation in Aspergillus nidulans

SummaryA diploid strain of Aspergillus nidulans with two heteroallelic mutations in the pabaA cistron (right arm of the first chromosome) has been studied. Part of the paba-independent colonies which have been examined was heterogeneous, i.e. they showed conidia of different colour and genotype. The genetic analysis of the various type of these heterogeneous colonies leads to the conclusion that, in Aspergillus nidulans, mitotic intragenic recombination is, in most cases, consequence of a single-strand break and exchange followed by the formation of a very long hybrid-DNA region (in our case a maximum of 22 meiotic units); the selected characteristics arise mainly by gene-conversion.Furthermore, data show a high negative interference between the selected crossing-over and a second crossing-over on the left arm and probably also on different chromosomes. The latter exchange occurs, as the former, between subchromatidic units.

Induction of cytoplasmic “petite” mutation by antibacterial antibiotics

Abstract The induction of petite mutation by three antibiotics known to inhibit microbial protein synthesis has been studied in two strains of yeast. Erythromycin and tetracycline, but not chloramphenicol, were affective in inducing petites. However, the two strains studied showed a considerable difference in sensitivity to the mutagenic action of the antibiotics used.

Tryptophan production by mutant strains of Escherichia coli K12.

In questa ricerca è stata messa a punto una tecnica per ottenere ceppi diE. coli produttori di quantità relativamente alte di triptofano. In un primo passo, sono stati selezionati mutanti diE. coli resistenti al 5-metiltriptofano, capaci di produrre triptofano in quantità misurabili. In un secondo passo mutativo si è aumentata la produzione di triptofano per una successiva selezione di mutanti resistenti al 5-fluoro-triptofano. La quantità di triptofano prodotta dai ceppi doppi mutanti è di circa dieci volte maggiore di quella dei singoli mutanti.

“Barriers” in intragenic mitotic crossing-over

Abstract The left arm of the first chromosome of Aspergillus nidulans has been analyzed by studying the effects of intragenic and intergenic mitotic crossing-over. The segregation following intragenic crossing-over is interrupted by a “barrier” which is distal to riboI . Following a reciprocal recombination in the gene pfp proximal to riboI , the far distal marker su Iad20 always remains in the parental condition. Intergenic crossing-over produces the results expected on the basis of classical theories. Intragenic recombination selected on the left arm produces a strong negative interferenc in the right arm which is probably due to “intragenic type” of crossing-over. Evidence for a second barrier has been found in the right arm of the first chromosome.

A quick method for testing recessive lethal damage with a diploid strain of Aspergillus nidulans

A simple method capable of detecting recessive lethal damage in a diploid strain of Aspergillus nidulans is described. The method scores the recessive lethals on the 1st, the 3rd and the 5th chromosomes, which represent about 40% of the total map of A. nidulans. Two examples of induced lethals, with ultraviolet irradiation and methyl methanesulfonate are shown. The frequency of lethals may reach 36% of the total population with UV irradiation.

MITOTIC RECOMBINATION AND MUTATION.

Abstract It has been shown that intragenic mitotic recombinants in the pfp gene in Aspergillus nidulans derive both by a reciprocal and a non-reciprocal process. Reciprocal recombination usually modifies the genes in both the strands involved; on the other hand non-reciprocal recombination does not modify the gene.