A new class of p-fluorophenylalanine-resistant mutants in Neurospora crassa

Isolation and characterization of a new class of amino-acid-analogue-resistant mutants inAspergillus nidulansusing reduced carbon flow

Four recessive amino-acid-analogue-resistant mutants were isolated on a medium containing acetate as the sole carbon source and the amino acid analogues p-fluorophenylalanine and ethionine. None of the mutants showed any growth requirement. Analysis of growth on media containing an amino acid as the sole nitrogen source indicated that two mutants out of the four possess normal systems for utilization of acidic, neutral, basic and aromatic amino acids. The mutantsfpa70 andfpa71 showed reduced growth on tryptophan as the sole source of nitrogen. Three new loci, identified after preliminary genetic analysis, were located on three linkage groups: one each on linkage groups I, VI and VIII.

Six new loci controlling resistance top-fluorophenylalanine inAspergillus nidulans

Twelve FPA-resistant mutants were selected on medium containingp-fluorophenylalanine and ethionine. Dominance tests in heterozygous diploids showed that 8 out of 12 are dominant and 4 recessive to their wild-type alleles. One mutant,fpa60, showed a partial requirement for tyrosine and was found to be allelic to anfpaAmutant described previously. A tyrosine non-requirer,fpa65, was also assigned to this locus. The other 10 mutants did not show any growth requirement and were simultaneously resistant to ethionine and 3-amino-L-tyrosine. Of the 8 dominant mutants, 3 were allelic to the permease-mutants at the locusfpaD.Dominant mutants showed higher degrees of resistance than recessive ones. Six new loci, identified after preliminary genetic analysis, were located on 3 linkage groups: 3 on linkage group VI, and one each on linkage groups I, V, and VIII. The recombinantfpaD11;fpaK69 was found to be sensitive to FPA.

Regulation of tryptophan biosynthesis in Saccharomyces cerevisiae: mode of action of 5-methyl-tryptophan and 5-methyl-tryptophan-sensitive mutants

In a wild-type strain of Saccharomyces cerevisiae the tryptophan analogue dl-5-methyl-tryptophan (5MT) causes only a slight reduction of the growth rate. Uptake experiments indicate that the limited inhibition is partly due to low levels of 5MT inside the cell. On the other hand, this low concentration of 5MT leads to an increase in the activity of the tryptophan-biosynthetic enzymes. Evidence is presented that suggests that 5MT acts primarily through feedback inhibition of anthranilate synthase, the first enzyme of the pathway. A number of 5MT-sensitive mutants have been isolated, characterized, and assigned to one of the following three classes: class I, strains with altered activity and/or feedback sensitivity of anthranilate synthase; class II, strains with elevated uptake of 5MT; class III, mutants with altered regulation of the tryptophan-biosynthetic enzymes, which do not exhibit increases in activity in the presence of 5MT. This failure to exhibit increased enzyme activities in mutants of class III can also be observed after tryptophan starvation. Two mutants of class III show high sensitivity towards 3-amino-1,2,4-triazole. They can not exhibit derepression of some histidine- and arginine-biosynthetic enzymes under conditions that lead to an increase in these same enzymes in the wild-type strain.

Cold-sensitive mutants of Neurospora crassa

Cold-sensitive mutants of the eucaryote Neurospora crassa have been isolated by a modification of the filtration-enrichment technique of Catcheside. The mutants include osmotic remedial, auxotrophic, transport, and incorporation deficient isolates.