Showing papers by "Vrije Universiteit Brussel published in 1972"
TL;DR: The hypothesis that argE and argCBH form two operons transcribed in opposite directions from an internal promoter-operator complex is discussed, and it is suggested that a secondary promoter exists at or near the argB-H boundary.
Abstract: In Escherichia coli K12, four of the nine structural genes involved in the biosynthesis of arginine (argE, C, B and H) form a tight cluster within which a clockwise-polarized unit of expression (argCBH) had previously been identified. From a mutant carrying an argCB deletion that greatly lowers the rate of expression of argE but falls short of known argE markers, we have isolated several derivatives in which the expression of argE is partly restored. In about a third of these strains repression of both E and H enzymes by arginine is almost abolished. The mutations responsible appear to be cis-dominant and to map to the right of argE, probably between argE and C. One mutant in which control of argE alone is affected has also been found; it is shown to carry a duplication of argE in addition to the argCB deletion of the parental strain. We discuss the hypothesis that argE and argCBH form two operons transcribed in opposite directions from an internal promoter-operator complex. It is also suggested that a secondary promoter exists at or near the argB-H boundary.
72 citations
TL;DR: Alteraction of the arginine pathway regulatory gene, argR, was shown to reduce the repressibility of the enzyme by both end products while mutations affecting uridine monophosphate pyrophosphorylase (upp) besides affecting uracil uptake preclude enzyme repression by urACil or cytosine in the biosynthesis of carbamoylphosphate and the pyrimidines.
Abstract: In the course of experiments directed towards the isolation of mutants of Escherichia coli K12 with altered regulation of the synthesis of carbamoylphosphate synthetase, two types of mutations were found to affect the cumulative repression of this enzyme by arginine and uracil. Alteraction of the arginine pathway regulatory gene, argR, was shown to reduce the repressibility of the enzyme by both end products while mutations affecting uridine monophosphate pyrophosphorylase (upp) besides affecting uracil uptake preclude enzyme repression by uracil or cytosine in the biosynthesis of carbamoylphosphate and the pyrimidines. The upp mutations were located on the chromosome near the gua operon. Mutations previously designated as uraP are shown to belong to this class.
44 citations
TL;DR: The NMR study of a large number of mixed tetraorganotins shows that the J vs Σσ * relationship is invalid, even in the mixed tetrasetraalkyltin series as mentioned in this paper.
24 citations
17 citations
TL;DR: The yolk DNA is an endogenous component of the yolk platelets of Xenopus laevis oocytes and Cytochemical and biochemical controls preclude the possibility that the yolks might be contaminated by nuclear or mitochondrial DNA.
Abstract: High molecular weight DNA was isolated from the yolk platelets of Xenopus laevis oocytes ovulated in vitro. Yolk DNA has the same buoyant density in CsCl gradients as mitochondrial and nuclear DNAs, and, like them, it is double-stranded. Yolk DNA behaves like nuclear DNA, and not like mitochondrial DNA, upon renaturation after denaturation. The molecules are always linear. Cytochemical and biochemical controls preclude the possibility that the yolk DNA might be contaminated by nuclear or mitochondrial DNA. We conclude that the yolk DNA is an endogenous component of the yolk platelets.
14 citations
TL;DR: In this article, the combinatorial method of Nagle for monomer-dimer mixtures is extended to the monomer -trimer case, where the relevant graphs involve two different types of edges and their weights are complicated functions of the natural expansion variable x of the problem.
Abstract: The combinatorial method of Nagle for monomer—dimer mixtures is extended to the monomer—trimer case. It turns out that the method becomes much more sophisticated: the relevant graphs involve two different types of edges and their weights are complicated functions of the natural expansion variable x of the problem (related to the trimer concentration). The method is applied to assemblies of (a) rectilinear, (b) bent, and (c) flexible trimers on the square lattice. The residual entropy of rectilinear trimers at close packing is estimated, SR/k=0.45.
13 citations
TL;DR: In this paper, an automatic method involving an Auto analyzer system for the direct potentiometric determination of sodium in river and mineral waters is presented, and the accuracy and reproducibility of the system proved to be excellent.
Abstract: An automatic method involving an Auto analyzer system for the direct potentiometric determination of sodium in river and mineral waters is presented. The accuracy and reproducibility of the system proved to be excellent.
13 citations
TL;DR: In this paper, the CMR spectra of the following bicyclo[2, 2,2,2] octane compounds were measured: 1-azabicyclo[1, 2] octan-3-one (1), 2-zabicyclecyclo[ 2, 2.2]octaone (2), 3-ethylidene-1-abicycleclo-[1, 3, 2]-octane (3, 2], octane-2-ene (2, 3-1), and the Z and E configuration
Abstract: CMR spectra of the following bicyclo[2,2,2]octane compounds were measured: 1-azabicyclo[2,2,2]octan-3-one (3), 2-azabicyclo[2,2,2]octan-3-one (5), bicyclo[2,2,2]octaone (4), 3-ethyl-1-azabicyclo[2,2,2]oct-2-ene (6) and of the Z and E isomers of 3-ethylidene-1-azabicyclo-[2,2,2]octane (1 and 2). The attribution of the signals and confirmation of the Z and E configuration of isomers (1) and (2) is described.
12 citations
TL;DR: It is shown by means of physical arguments, how one can reduce the diffusion equation to a simple one-dimensional form by a stochastic simulation, which is easily realized on a digital computer.
12 citations
9 citations
TL;DR: In this paper, two 4b 5,6,7,8,8a,10,11,16,16b-decahydrodibenz[f,h]indolo-[2,3-a]quinolizine epimers have been synthesized starting from trans-1, 2, 3, 4, 4a, 10b-hexahydrophenanthridine.
TL;DR: The non-markovian time evolution of a weakly coupled homogeneous gravitational system was shown by Prigogine and Severne to present a steady creation of correlation energy superposed upon weakly oscillatory relaxation process.
TL;DR: The conformational energy of the central double pentapeptide of the human IgG1 hinge region Cys- pro-pro-cys-pro has been calculated with the aid of semi-empirical potential functions and it was found that a small number of families of similar backbone conformations is allowed for the chains of the cycle.
TL;DR: In this article, a study about the biotope of the ostreiculture, the "Bassin de Chasse d'Ostende", has been conducted, and it has shown that: 1) the phyto-and zooplanktonic population extraordinary abundant let suppose us that the available food is enormous 2) the harmful organisms (Polydora ciliata) and the competitors of food for the oyster (Mytilus edulis, Balanus, Mya arenaria) have fixed them by a clumsy manner on the ostrea
TL;DR: The non-linear elastic constitutive equations proposed by Kauderer, [1], are a particular case of a class of quasi-linear equations as mentioned in this paper, and they cannot give an account of some specific nonlinear effects of the Poynting and the Kelvin types.
Abstract: The non-linear elastic constitutive equations proposed by Kauderer, [1], are a particular case of a class of quasi-linear equations. They cannot give an account of some specific non-linear effects of the Poynting and the Kelvin types. It is more useful in two and three dimensional problems to start with general non-linear forms proposed initially by Brillouin, [2].
01 Jan 1972
TL;DR: In this paper, the Jones and Mueller matricial descriptions of optical properties, particularly adapted to this type of devices, are introduced, and for three classes of problems the complete determination of optical characteristics using matrix formalisms is performed.
Abstract: Progress in generalized and three dimensional photoelas-ticity needs accurate specification of numerous and complex polarization changing devices. The Jones and Mueller matricial descriptions of optical properties, particularly adapted to this type of devices, are introduced. For three classes of problems the complete determination of optical characteristics using matrix formalisms is performed. The numerical programs, based on the matricial description and permitting effective specification of large numbers of systems, are also showed and discussed.
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TL;DR: Autoradiography of C-14 labelled phytoplankton collected onto a millipore filter allows the determination of the number of photosynthetically active cells in a water sample and thus gives useful information on the standing crop in primary production studies.