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G Lester

Publications and source records attributed to G Lester.

33 records · Page 2Linked to original sources
PubMed1968

In vivo regulation of intermediate reactions in the pathway of tryptophan biosynthesis in Neurospora crassa.

The in vivo regulation of intermediate reactions in the pathway of tryptophan synthesis in Neurospora crassa was examined in a double mutant (tr-2, tr-3) which lacks the functions of the first and last enzymes in the pathway from chorismic acid to tryptophan. The double mutant can convert anthranilic acid to indole and indole-3-glycerol, and the production of these indolyl compounds by germinated conidia was used to estimate the activity of the intermediate enzymes in the pathway. Indole-synthesizing activity was maximal in germinated conidia obtained from cultures in which the levels of l-tryptophan were growth-limiting; the formation of this activity was markedly repressed when the levels of l-tryptophan exceeded those required for maximal growth. d-, 5-methyl-dl-, and 6-methyl-dl-tryptophan were less effective than l-tryptophan, and 4-methyl-dl-tryptophan, tryptamine, and indole-3-acetic acid were ineffective in repressing the formation of indole-synthesizing activity; anthranilic acid stimulated the formation of indole-synthesizing activity. Preformed indole-synthesizing activity was strongly and specifically inhibited by low levels of l-tryptophan; several related compounds were ineffective as inhibitors. These results suggest that, in addition to repression, an end product feedback inhibition mechanism is operative on an intermediate enzyme(s) in tryptophan biosynthesis. The relation of these results to other in vivo and in vitro studies and to general aspects of the regulation of tryptophan biosynthesis in N. crassa are discussed.

Enzyme Repression↗
PubMed1966

Studies on insulin biosynthesis. Subcellular distribution of leucine-H3 radioactivity during incubation of goosefish islet tissue.

Islet tissue from the goosefish (Lophius piscatorius) was incubated in the presence of leucine-H(3). The tissue was then separated into subcellular fractions and the radioactivity determined in total acid alcohol-soluble proteins, insoluble proteins, and insulin. At any time, microsomal protein had a higher activity than secretion granule protein. Pulse-chase experiments further suggest the microsomes as primary sites of protein synthesis. The data are evidence for microsomal synthesis of insulin and for its subsequent transfer into the secretion granules.

Animals↗
PubMed1966

Genetic control of amino acid permeability in Neurospora crassa.

Lester, Gabriel (Reed College, Portland, Ore.). Genetic control of amino acid permeability in Neurospora crassa. J. Bacteriol. 91:677-684. 1966.-Strains of Neurospora 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 aberrant mt 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. The mt 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 alpha-aminoisobutyric acid. No difference was observed between strains carrying either mt allele in their ability to take up glucose; also, the uptake of anthranilic acid or of indole was not sufficiently impaired by the aberrant mt gene to prevent these tryptophan precursors from satisfying the nutritional requirement of certain tryptophan auxotrophs. The role of the mt gene in determining the permeability of N. crassa to amino acids is discussed.

Amino Acids↗
PubMed1965

Inhibition of Growth, Synthesis, and Permeability in Neurospora crassa by Phenethyl Alcohol.

Lester, Gabriel (Reed College, Portland, Ore.). Inhibition of growth, synthesis, and permeability in Neurospora crassa by phenethyl alcohol. J. Bacteriol. 90: 29-37. 1965.-Inhibition of the growth of Neurospora crassa in still culture was detected at 0.05% and was complete at a level of 0.2% phenethyl alcohol (PEA). Benzyl alcohol was less inhibitory, and 3-phenyl-1-propanol and phenol were more inhibitory, than PEA; benzylamine and phenethylamine were less inhibitory than the analogous hydroxylated compounds. Inhibition by PEA was not reversed by synthetic mixtures of purines and pyrimidines or vitamins, or by casein digests, yeast extract, or nutrient broth. The germination of conidia was inhibited by PEA, but after an exposure of 8.5 hr no loss of viability was observed. The addition of PEA to growing shake cultures caused a simultaneous inhibition of growth and of the syntheses of ribonucleic and deoxyribonucleic acids and protein; the relationships of these compounds to mycelial dry weight and to one another were constant in growing mycelia, and PEA did not significantly affect these relationships. PEA partially inhibited the uptake of glucose, but severely restricted the accumulation of l-leucine, l-tryptophan, or alpha-aminoisobutyric acid in germinated conidia. The efflux of alpha-aminoisobutyric acid from germinated conidia was somewhat enhanced by PEA, but this effect was not so pronounced as the (complete) inhibition of alpha-aminoisobutyric acid accumulation by PEA. It is suggested that PEA affects primarily the initial influx of alpha-aminoisobutyric acid rather than the subsequent retention of alpha-aminoisobutyric acid.

Journal Article↗
PubMedDate not supplied

State disparities in the diagnosis and placement of pupils with learning disabilities.

We investigated the hypothesis that interstate disparities in the diagnosis of pupils with learning disabilities (LD) are more strongly correlated with demographic and sociopolitical factors than with the biological prevalence of the disability. We also investigated the relationship of these factors to placement practices. Thirteen independent variables representing state characteristics were simultaneously regressed against each of seven static dependent variables, measuring diagnostic and placement practices in 1989, and two dynamic dependent variables, measuring changes in practices between 1976 and 1989. Results of the regression indicated that although demographic and sociopolitical factors explained none of the total prevalence of the four most common physical disabilities (adjusted R2[R2] = 0), they did explain to a moderate degree the state prevalence of LD (R2 ranged from .15 to .28), and were more predictive still depending on measure of LD prevalence. Moreover, these same factors strongly predicted the extent to which states mainstreamed their pupils (R2 = .59) and the size of the nonmainstreamed cognitively disabled (LD and educable mentally retarded) population (R2 = .56).

Adolescent↗