Genetic Control of Amino Acid Permeability in Neurospora crassa

Lester, Gabriel (Reed College, Portland, Ore.). Genetic control of amino acid permeability inNeurospora crassa . J. Bacteriol.91: 677–684. 1966.—Strains ofNeurospora crassa resistant to 4-methyltryptophan (4-MT) were isolated from populations of conidia exposed to ultraviolet light. In genetic crosses, 4-MT resistance behaved as a single-gene difference. Resistance to 4-MT could not be attributed to a relaxation of control of the formation or the activity of the enzymes of tryptophan biosynthesis. Growth studies involving tryptophan auxotrophs carrying the aberrantmt gene and uptake studies with normal and 4-MT-resistant strains showed that 4-MT resistance could be attributed to an inability of 4-MT-resistant strains to take up tryptophan and its methyl analogues. Themt gene is not specific for tryptophan; strains resistant to 4-MT are also resistant to ethionine, and they have a markedly reduced ability to take up serine, leucine, and α-aminoisobutyric acid. No difference was observed between strains carrying eithermt allele in their ability to take up glucose; also, the uptake of anthranilic acid or of indole was not sufficiently impaired by the aberrantmt gene to prevent these tryptophan precursors from satisfying the nutritional requirement of certain tryptophan auxotrophs. The role of themt gene in determining the permeability ofN. crassa to amino acids is discussed.