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At least 73 records · Page 4Linked to original sources
PubMed1972

Regulation of exocellular proteases in Neurospora crassa: induction and repression of enzyme synthesis.

Neurospora crassa strain 74A grown on Vogel's medium containing bovine serum albumin (BSA) as principal carbon source secretes proteolytic enzymes which appear in the culture filtrate. Low concentrations of sucrose (0.1%) are necessary for growth from conidia, as conidia will not germinate on BSA alone. Once growth is initiated, however, protease production begins and at 5 to 6 hr growth and enzyme production are parallel. Higher concentrations of sucrose (0.5-2%) repress protease synthesis. Other metabolizable materials (sugars, amino acids, peptide mixtures) also repress protease synthesis. Some sugars will not sustain growth but allow germination and full induction of protease in the presence of protein. A material found in culture fluids of cells during induction of protease synthesis when added to repressed cultures causes a five-fold increase in the amount of protease production, although this is still approximately half that of normally induced cells. This material appears to be produced by induced cells in as little as 2 hr of culture, which is before detectable levels of protease can be found. It is heat-stable, of low molecular weight, and is not a simple product of protein digestion by the N. crassa proteases.

Amino Acids↗
PubMed1977

Increased and decreased sensitivity to carbon catabolite repression of enzymes of acetate metabolism in mutants of Aspergillus nidulans.

The creA204, creB15 and creC27 mutations have been shown to cause carbon catabolite derepression of acetly CoA synthase and isocitrate lyase in Aspergillus nidulans. A recessive mutation, cre-34, which is linked to the creC gene, results in these enzymes being more sensitive than cre or wildtype strains to catabolite repression. The acetamidase levels of strains containing cre mutations have been investigated and provide support for the hypothesis that an acetate metabolite, rather than acetamide, induces this enzyme.

Acetate-CoA Ligase↗
PubMed1967

The regulatory process in the de-repression of enzyme synthesis. Alkaline phosphatase of Bacillus subtilis.

1. The kinetics of de-repression of alkaline phosphatase in Bacillus subtilis were studied after the removal of P(i). Enzyme activity appeared about 10min. after removal of P(i), whereas ;enzyme-forming potential' appeared after 6min. 2. Protein synthesis is not impaired for at least 20min. on removal of P(i), but RNA synthesis is considerably diminished. 3. Adding chloramphenicol to cells without P(i), just at the time they start to make enzyme-forming potential, does not affect the differential rate of enzyme synthesis compared with total protein. Enzyme-forming potential accumulates to about normal levels in the presence of chloramphenicol, even though peptide-bond formation is inhibited by more than 95%. 4. Similar experiments performed with actinomycin C show more complex effects. Actinomycin initially prevents RNA synthesis and also the synthesis of enzyme-forming potential. After some minutes RNA synthesis resumes at a low rate, to be followed 4min. later by enzyme synthesis. Enzyme-forming potential can accumulate in the presence of actinomycin after the resumption of RNA synthesis. Protein synthesis, initially inhibited by actinomycin as a consequence of the effect on RNA synthesis, is later directly inhibited by actinomycin. 5. Adding actinomycin to de-repressed cells already making enzyme stops enzyme synthesis within 4-5min. Enzyme synthesis resumes, as before, 4min. after the resumption of RNA synthesis. 6. Adding P(i) together with actinomycin to de-repressed cells synthesizing enzyme does not result in a lower yield of enzyme compared with actinomycin alone. 7. Actinomycin is less effective an inhibitor of RNA and protein synthesis in P(i)-starved cells if P(i) is also added. 8. These results are discussed in view of the three main models for the regulation of enzyme induction: regulation at the level of transcription only, at translation only, or a coupled model in which transcription requires concomitant translation. It is concluded that the present evidence most powerfully supports the model of transcriptional regulation.

Alkaline Phosphatase↗
PubMed1998

Repression of enzymes of the pentose phosphate pathway by glucose in fission yeast.

We examine here the effect of carbon sources on the synthesis of the shunt pathway enzymes in the fission yeast Schizosaccharomyces pombe growing on a mixture of ethanol and glycerol. Delta-gluconolactone induces practically every one of these enzymes. Glucose in contrast tends to attenuate the synthesis of the majority of them. RNA analysis confirms that their induction and repression reflect changes in the levels of their transcripts.

Enzyme Induction↗
PubMed1973

Repression of enzyme synthesis of the pyrimidine pathway in Salmonella typhimurium.

It has been reported by other workers that a uridine and probably also a cytidine nucleotide are required for maximal repression of aspartate transcarbamylase encoded by the gene pyrB in Salmonella typhimurium. We have identified the repressing metabolites for three more biosynthetic enzymes, namely, dihydroorotate dehydrogenase (encoded by pyrD), orotidine-5'-monophosphate pyrophosphorylase (encoded by pyrE), and orotidine-5'-monophosphate decarboxylase (encoded by pyrF), as well as examining the repression profiles of aspartate transcarbamylase in more detail. Using a specially constructed strain of S. typhimurium (JL1055) which lacks the enzymes for the interconversion of cytidine and uridine compounds, thus allowing the independent manipulation of endogenous cytidine and uridine nucleotides, we found that a cytidine compound is the primary effector of repression in all cases except for aspartate transcarbamylase where little repression is observed in excess cytidine. For aspartate transcarbamylase, we found that the primary repressing metabolite is a uridine compound.

Arginine↗
PubMed1972

Repression of enzymes of arginine biosynthesis by L-canavanine in arginyl-transfer ribonucleic acid synthetase mutants of Escherichia coli.

We show that the arginine analogue, l-canavanine, repressed the accumulation of translatable messenger ribonucleic acid (RNA) for three arginine biosynthetic enzymes in Escherichia coli. The method used to determine the level of translatable messenger RNA depended upon measurement of a burst of enzyme synthesis as described previously. E. coli strains with defective arginyltransfer ribonucleic acid (tRNA) synthetase (argS mutants) were insensitive to canavanine repression. When deprived of leucine, a leu argS strain regained normal sensitivity to canavanine repression. The level of in vivo canavanyl-tRNA(arg) was determined for a normal strain and an argS mutant. After 20 min of growth with canavanine only 9% of tRNA(arg) from the argS strain was protected from periodate oxidation, while 42% of the tRNA(arg) from an argS(+) strain was charged. When deprived of leucine, leu argS or leu argS(+) strains grown with canavanine contained more than 60% charged tRNA(arg). Reverse phase column chromatography of periodate-oxidized tRNA from canavanine-grown argS and argS(+) strains showed no preferential charging of any isoaccepting species of tRNA(arg). Therefore, we failed to detect a specific arginyl-tRNA species that might be involved in repression by canavanine. However, the data suggest that canavanine repression of the arginine pathway occurs only when high levels of canavanyl-tRNA are present, and thus support the notion that arginyl-tRNA synthetase plays a role in generating a repression signal.

Acylation↗
PubMed1990

Factors influencing extracellular protease synthesis in an Aspergillus flavus isolate.

Our studies on the control of extracellular protease synthesis in an Aspergillus flavus strain isolated by us indicate that in a defined medium a protein must be present for enzyme to be produced. Soya bean protein and cotton seed protein were efficient inducers. The ability to induce enzyme synthesis was a characteristic property of the individual protein. Enzyme activity was not derepressed in the absence of a protein by limitation of nutrients. Cycloheximide blocked enzyme synthesis. Low levels (1%) of various carbohydrates did not repress enzyme synthesis, whereas most carbohydrates at 3% levels repressed enzyme synthesis. Addition of glucose to cultures actively producing the enzyme blocked further synthesis of enzyme. Addition of glucose to cultures producing the enzyme in the absence of sodium nitrate resulted in a decrease of enzyme activity.

Aspergillus flavus↗
PubMed1976

Production of extracellular ribonuclease by yeasts and yeastlike fungi, and its repression by orthophosphate in species of Cryptococcus and Tremella.

A strain of Cryptococcus laurentii and a haploid isolate of Tremella foliacea were shown to produce orthophosphate-repressible ribonuclease in liquid culture. Addition of as little as 1 mM K2HPO4, pH 7.0, completely repressed enzyme production by both fungi. The orthophosphate-repressible enzyme was not produced by other species of the two genera tested. These results, together with other findings, suggest a close phylogenetic relationship between Cryptococcus laurentii and Tremella foliacea. The ability of other yeasts and yeastlike fungi to hydrolyze ribonucleic acid in a solid test medium was assessed. Based on the limited number of organisms available for study, extracellular ribonuclease activity was found in species having close affinity to the Basidiomycetes and in yeasts classified in the ascomycetous genera, Endomycopsis, Hansenula, and Kluyveromyces. Other ascomycetous yeasts did not exhibit extracellular ribonuclease.

Ascomycota↗
PubMed1984

Identification of new genes involved in the regulation of yeast alcohol dehydrogenase II.

Recessive mutations in two negative control elements, CRE1 and CRE2, have been obtained that allow the glucose-repressible alcohol dehydrogenase (ADHII) of yeast to escape repression by glucose. Both the cre1 and cre2 alleles affected ADHII synthesis irrespective of the allele of the positive effector, ADR1. However, for complete derepression of ADHII synthesis, a wild-type ADR1 gene was required. Neither the cre1 nor cre2 alleles affected the expression of several other glucose-repressible enzymes. A third locus, CCR4, was identified by recessive mutations that suppressed the cre1 and cre2 phenotypes. The ccr4 allele blocked the derepression of ADHII and several other glucose-repressible enzymes, indicating that the CCR4 gene is a positive control element. The ccr4 allele had no effect on the repression of ADHII when it was combined with the ADR1-5c allele, whereas the phenotypically similar ccr1 allele, which partially suppresses ADR1-5c, did not suppress the cre1 or cre2 phenotype. Complementation studies also indicated that ccr1 and snf1 are allelic. A model of ADHII regulation is proposed in which both ADR1 and CCR4 are required for ADHII expression. CRE1 and CRE2 negatively control CCR4, whereas CCR1 is required for ADR1 function.

Alcohol Dehydrogenase↗
PubMed1983

Possible role of a regulatory gene product upon the myo-inositol-1-phosphate synthase production in Neurospora crassa.

The regulatory effect of inositol on inositol-1-phosphate synthase in Neurospora crassa strains was studied. Inositol represses enzyme production in the cultures of the wild type and that of the thermosensitive inositol-requiring mutant grown at 22 degrees C. Enzyme activity as well as the quantity of enzyme protein decreased sharply in both strains by increasing concentrations of inositol in the medium. Inositol-requiring strains used in our experiments can be divided into two groups. The first group produces a protein related immunologically to inositol phosphate synthase, but which is enzymatically inactive. The synthesis of this defective enzyme was also repressed by inositol. In the second group, this protein was found to be completely lacking, in both the thermosensitive mutant grown at 37 degrees C, and in a strain requiring inositol due to a reciprocal translocation. The thermostability and the cross immunoelectrophoresis of the enzyme suggest that in the case of the thermosensitive inositol-requiring mutant, the mutation did not occur in the structural gene of the enzyme, but its regulation was probably affected.

Carbohydrate Epimerases↗