Showing papers on "Psychological repression published in 1971"

Methionine-Mediated Repression in Saccharomyces cerevisiae: a Pleiotropic Regulatory System Involving Methionyl Transfer Ribonucleic Acid and the Product of Gene eth2

Abstract: Detailed study of methionine-mediated repression of enzymes involved in methionine biosynthesis in Saccharomyces cerevisiae led to classification of these enzymes into two distinct regulatory groups. Group I comprises four enzymes specifically involved in different parts of methionine biosynthesis, namely, homoserine-O-transacetylase, homocysteine synthetase, adenosine triphosphate sulfurylase, and sulfite reductase. Repressibility of these enzymes is greatly decreased in strains carrying a genetically impaired methionyl-transfer ribonucleic acid (tRNA) synthetase (mutation ts(-) 296). Conditions leading to absence of repression in the mutant strain have been correlated with a sharp decrease in bulk tRNA(met) charging, whereas conditions which restore repressibility of group I enzymes also restore tRNA(met) charging. These findings implicate methionyl-tRNA in the regulatory process. However, the absence of a correlation in the wild type between methionyl-tRNA charging and the levels of methionine group I enzymes suggests that only a minor iso accepting species of tRNA(met) may be devoted with a regulatory function. Repressibility of the same four enzymes (group I) was also decreased in strains carrying the regulatory mutation eth2(r). Although structural genes coding for two of these enzymes, as well as mutations ts(-) 296 and eth2(r) segregate independently to each other, synthesis of group I enzymes is coordinated. The pleiotropic regulatory system involved seems then to comprise beside a "regulatory methionyl tRNA(met)," another element, product of gene eth2, which might correspond either to an aporepressor protein or to the "regulatory tRNA(met)" itself. Regulation of group II enzymes is defined by response to exogenous methionine, absence of response to either mutations ts(-) 296 and eth2(r), and absence of coordinacy with group I enzymes. However, the two enzymes which belong to this group and are both involved in threonine and methionine biosynthesis undergo distinct regulatory patterns. One, aspartokinase, is subject to a bivalent repression exerted by threonine and methionine, and the other, homoserine dehydrogenase, is subject only to methionine-mediated repression. Participation of at least another aporepressor and another corepressor, different from the ones involved in regulation of group I enzymes, is discussed.

The Arginine Biosynthetic System and Its Regulation

Abstract: Publisher Summary This chapter discusses the arginine biosynthetic system and its regulation of action. There is a substantial amount of evidence supporting the idea of translational repression by arginine in Escherichia coli. Moreover, the available quantitative indications make it appear that the translational mechanism accounts for arginine repression to a major extent, if not entirely. A precise model of translational repression cannot be presented yet with assurance; however, the notion of the repressive complex has gained some definition, and it is possible to make surmises on the functioning of the complex in triggering repression. It is not a foregone conclusion that all repressions by amino acids proceed in exactly the same manner, but in those cases where aminoacyl-tRNA synthetases are involved, it is attractive to assume that aminoacyl–tRNAs are also involved, because a means for the specificity of repression might then be provided. The aminoacyl-tRNA could be pictured as recognizing its codon, at a suitable position in the message, and as participating there, together with the corresponding synthetase and the other required components, in the formation of the repressive complex. This repression would be specific for the amino acid corresponding to the codon recognized. With or without the involvement of aminoacyl–tRNA, it seems likely that the free amino acid constitutes a part of the repressive complex. The complex may distort, or otherwise affect the ribosome and expose the message to attack by a nuclease.

Catabolite Repression in the d-Serine Deaminase System of Escherichia coli K-12

Abstract: The induced synthesis of d-serine deaminase in Escherichia coli is subject to three catabolic effects: inhibition on inducer uptake, transient repression, and catabolite repression. Inhibition on d-serine uptake is not significant at the d-serine concentration normally used for induction. Transient repression and catabolite repression of d-serine deaminase synthesis are abolished by mutations in dsdCy, which appears to be an operator locus. The decline in the rate of constitutive synthesis observed in dsdCx mutants growing with glycerol as carbon source at temperatures above 37 C is due to catabolite repression. The low level of constitutivity at 37 C and the partial cis dominance of dsdCx mutants are not artifacts of catabolite repression. It is suggested that a product of one of the genes of the dsd operon may regulate the expression of the operon.

Induction and repression of L-arabinose isomerase in Salmonella typhimurium.

Abstract: As with other inducible enzymes, the induced synthesis of l-arabinose isomerase (l-arabinose ketol isomerase, EC 5.3.1.4) in Salmonella typhimurium is subject to catabolite repression. Of the three catabolite repressors tested, glucose produces maximum repression. Analogues of catabolite repressors like 2-deoxy-d-glucose and d-fucose also inhibit the synthesis of the enzyme. The catabolite repression is completely reversed in the presence of 1.5 × 10−3m cyclic 3′,5′-adenosine monophosphate (AMP). The maximum repression is produced in glucose-grown cells in glucose-containing induction medium. Cyclic 3′,5-AMP reverses this repression provided that the cells are treated with ethylenediaminetetraacetic acid (EDTA). In normal cells, cyclic 3′,5′-AMP has no effect on the induction but in EDTA-treated cells the cyclic nucleotide enhances synthesis of the enzyme. The inhibition produced by d-fucose cannot be reversed by cyclic 3′,5′-AMP. d-Fucose competes with the inducer l-arabinose in some step(s) involved in the process of induction.

Effect of point mutations in the lac promoter on transient and severe catabolite repression of the lac operon of Escherichia coli.

Abstract: 1. Experiments were devised to show whether the point mutations L8 and L29 in the lac promoter alleviate transient repression. 2. Several recombinants were picked from matings between a single F(-)p(+) strain and Hfr strains carrying mutations L8 and L29. All of the 19 p(-) recombinants tested proved to suffer no transient repression, whereas all of the eight p(+) recombinants tested suffered prolonged transient repression. 3. A diploid strain was constructed in which more than 90% of the thiogalactoside transacetylase is synthesized from the episome with a wild-type lac promoter, whereas 100% of the beta-galactosidase is synthesized from the chromosome with a promoter carrying mutation L8. In this diploid the synthesis of thiogalactoside transacetylase suffered transient repression but the synthesis of beta-galactosidase did not. 4. Exactly similar results were obtained with a diploid strain in which the chromosomal promoter carried mutation L29. 5. The same diploid strains were used in experiments to show whether mutations L8 and L29 alleviate the severe catabolite repression caused by growth in glucose plus gluconate. In both strains glucose+gluconate repressed the synthesis of beta-galactosidase much less than the synthesis of thiogalactoside transacetylase. 6. These and previously reported results can be explained by assuming (a) that both mutations L8 and L29 render the lac promoter partially, but not completely, insensitive to catabolite repression, and (b) that transient repression is an exceptionally severe form of catabolite repression.