Constitutive synthesis

The Action of Alkaline Reagents on 2 3-1 6- and 3 4-l 6-Dianhydro-3-talose. A Constitutional Synthesis of Chondrosamine and other Amino-Sugar Derivatives, S. P. James, F. Smith, M. Stacey, and L. F. Wiggins, J. Chem. Soc., (1946) 625-628. 

A GALA mutation (GAL4C) leads to constitutive synthesis of the GALL gene product in haploid yeast. Propose an explanation for the effect of this mutation. 

Seven years later, in a critical review on the synthesis of peptides, the following statement was made "Chemists in particular should respect the classical criteria of what constitutes synthesis of a natural product, i.e., that synthesis of a natural product has been achieved, when the physical, chemical and biological properties of the synthetic compound match those of the natural prototype. Unfortunately not a single one of the "synthetic proteins" satisfies these criteria. It is frequently argued that these criteria are not applicable to more complex situations, but lowering standards of purity is not likely to advance the field. Presently available analytical methods cannot adequately detect inhomogeneity in a high molecular peptide that is produced by stepwise synthesis. Consequently, the synthetic method must be chosen so that the product can be purified and critically evaluated by the available analytical techniques. F.M. Finn, 1976). 

Constitution. Synthesis.—The constitution and synthesis of caoutchouc is connected with two of the terpene hydrocarbons previously mentioned. It has been stated that caoutchouc is a hydrocarbon of the composition (CsHg). As this is the formula for certain of the terpenes we should naturally expect to find that caoutchouc is itself a member of this group. 

GAL81 operator gene for GALA permits constitutive synthesis of enzymes controlled by GALA 342... 

A sequence of bases (in the DNA)—the operator lac o—is adjacent to the lac mRNA promoter and binds repressor. When the repressor protein is bound to the operator, attachment of RNA polymerase to the promoter is prevented by steric interference, and initiation of transcription of lac mRNA does not occur. A mutation in the operator, which eliminates repressor binding, also leads to constitutive synthesis. 

Pll. Pledger, W. J., Hart, C. A., Locatell, K. L., and Scher, C. D., Platelet derived growth Sictor-modulated proteins Constitutive synthesis by a transformed cell line. Proc. Natl. Acad. Sci. U.S.A. 78, 4358-4362 (1961). 

Further details of the pathways for the degradation of PAFIs are described in Chapter 6, Section 6.2.1 and in a review (Neilson and Allard 1998). It seems that most of the degradative enzymes are inducible, and this is consistent with the fact that most strains have been isolated after specific enrichment with the xenobiotic. The case of the partially constitutive synthesis of catechol 1,2-dioxygenase in the yeast Trichosporon cutaneum (Shoda and Udaka 1980) has been noted (Section 4.5.2). In the case of biotransformation, however, there are sporadic examples of the constitutive synthesis of enzymes. For example, the system carrying out the O-methylation of halogenated phenolic compounds was apparently constitutive (Neilson et al. 1988) this observation is consistent with the isolation of the strains by enrichment with Q compounds structurally unrelated to the halogenated substrates. The O-methylation reaction may function primarily as a detoxification system, so that in this case constitutive synthesis of the enzyme would clearly be advantageous to the survival of the cells. 

Figure 3 Regulation at the level of mRNA degradation. Genes that are regulated by differential mRNA stability usually have promoters (bent arrow) that are always active, resulting in constitutive synthesis of the full-length transcript (dotted line).

Hochheimer a, Hedderich R and Thauer RK (1998) Theformylmethanofuran dehydrogenase isoenzymes in Methanobacterium wolfd and Me-thanobacterium thermoautotrophicum induction of the molybdenum isoenzyme by molybdate and constitutive synthesis of the tungsten isoenzyme. Arch Microbiol 170 389-393. 

Lee, J.H., A. Hiibel, and E. Schoffl. 1995. Derepression of the activity of genetically engineered heat shock factor causes constitutive synthesis of heat shock proteins and increased thermotolerance in transgenic Arabidopsis. Plant J. 8 603-612. 

Su, J., and R. Wu. 2004. Stress-inducible synthesis of proline in transgenic rice confers faster growth under stress conditions than that with constitutive synthesis. Plant Sci. 166 941-948. 

A further test of the hypothesis was made in synchronized cells. The model predicts that if R production is prevented before G1 [3], the constitutive rate of enzyme synthesis should continue for some hours beyond G1 [3]. That this prediction is confirmed is also illustrated in Figure 7. Actinomycin D (or daunamycin or mithramycin) added to preinduced, synchronized cells early in G1 allows the constitutive synthesis of TAT to continue beyond G1 [3], as shown by the failure of the inducer requirement to develop at that time. Thus, during G2, M, and early Gl, when transcription of structural and regulatory genes is presumably repressed, control at the translational level does not take place. However, as the cells enter the phase of the cycle where transcription control is lifted, i.e., late Gl and S, translational regulation by R becomes important. TAT can be induced by the steroids only during this translation control period consistent with the idea that somehow the inducers interfere with the function of R, the labile inhibitor of translation. 

Yeast strains that carry a mutation at the adel2 locus are adenine-specific auxotrophs and accumulate inosine and h3T>oxanthine 114). In addition, the normal regulation of purine biosynthetic activity is modified toward constitutive synthesis, even in the presence of high levels of exogenous AMP 114, 115). 

AMD to mimic the effect of repressor. Not only does AMD not mimic the repressor, but it actually prolongs the period of constitutive synthesis of TAT [56]. Since the TAT repressor does specifically inhibit TAT synthesis but does not act at gene transcription, it must act on a posttranscriptional function in the expression of the gene for TAT structure. 

As cells enter G, the TAT templates which existed in the cell prior to Gj are being translated constitutively—that is, independent of the presence or absence of inducer. At Gi(3), when the S and R genes are again transcribed, the constitutive synthesis of TAT is terminated by the appearance of the R gene product—TAT repressor. If inducer is not present at that time, the synthesis of TAT is fully repressed and the activity declines to the basal level. If the inducer is present, the fully induced rate of TAT synthesis is reestablished, which, as in the E. coli lac system, is somewhat less than the constitutive rate [19], If the resumption of S and R gene transcription is prevented at G (3) by AMD, the repressor never reappears, and the constitutive synthesis of TAT from its preexisting, stable template is prolonged (Fig. 5). 

The operator is the site on the chromsome where the lac repressor is thought to bind, thereby inhibiting transcription. The combined length of the promoter operator region is about 100 nucleotides. Operator mutations (o ) result in a decreased ability of the operator to bind repressor and lead to constitutivity, which is the ability to synthesize the products of the operon in the absence of inducer. Levels of constitutive synthesis in o" mutants range from 2 to 30% of wild type, and addition of inducer can increase the enzyme synthesis to levels of the wild-type strain [29],... 

In any hypothesis concerning the nature of the operator, its specific complementary configuration must be genetically determined therefore the operator could be affected by mutations which would alter or abolish its specific affinity for the repressor. Such mutations might result in constitutive synthesis of the protein or proteins if no other functions were impaired. These mutations should define an operator locus the most distinctive predictable property of operator mutants is that the constitutive allele should be dominant to the wild type, since the repressor-sensitive operators should not prevent the functioning of repressor-insensitive operators. 

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