Site-directed mutants of the cAMP receptor protein-DNA binding of five mutant proteins

Oligonucleotide-directed mutagenesis was employed to generatemutants of the cAMP receptor protein (CRP) of Escherichia coli.The mutant proteins were purified to homogeneity and testedfor stability and DNA binding. It is shown that mutations atthe position of Arg¹⁸⁰ abolish specific DNA binding, whereasthose at the position Arg¹⁸⁵ have very little effect. Both positionshave previously been implicated as crucial for the specificinteraction between CRP and DNA. The Ser¹²⁸ Ala mutant showsa slight reduction in DNA binding affinity relative to wild-type.All mutants investigated show similar stability profiles towild-type CRP with respect to thermolysin proteolysis as a functionof temperature.     

Antimony removal from dilute solutions using a restrained bed electrochemical reactor

The electrochemical removal of Antimony from 1m sulphuric acid in a restrained bed reactor was studied in terms of current, flow velocity, bed depth, bead size and pressure drop. Current efficiencies are quoted as a function of current density and information is given so that they may be calculated in terms of the above variables. Experimentally-obtained limiting current densities are compared with calculated values, using empirical formulae from the literature.     

Identification and composition of turnip root lipids

Two varieties of turnip, Laurentian and Wye, were examined for their lipid and fatty acid composition. Lipids extracted with 80% ethanol contained variable quantities of phosphatidic acid, which was considered to be an artifact. Crude lipids were fractionated by TLC, and fatty acids and sterols were analyzed by GLC. Among the common phospholipids, cardiolipid and phosphatidyl glycerol were abundant components. Linolenic acid comprised 60% of the total fatty acids. β-Sitosterol was the principal sterol, and about half of the carotenoids was lycopene. No great differences between the two varieties studied were observed however. Contribution No. 53 of the Food Research Institute, Canada Department of Agriculture, Ottawa.     

Zur unverträglichkeit von polymergemischen. VII. Lichtstreuungsmessungen an quaternären und quintären polymer-systemen polymer(1)/polymer (2)/polymer(3)/benzol und polymer(1)/polymer(2)/polymer(3)/polymer (4)/benzol

A polystyrene of high molecular weight was investigated by means of light scattering in isoerefractive polymer/benzene mixtures. Two or three of the following polymers are used, which are isorefractive with benzene: polymethylmethacrylate (PMMA), polybutadienne (PB), and polyisobutene (PIB). It is possible to determine the degree of incompatibility of the ?unvisible”? polymers by a comparison of the ?-points of PS in the multi-component systems with the ?-points PS in the ternary systems PS/polymer(2)/benzene. In all cases it turned out, that the degree of compatibility of PS with the other polymers increased by a further addition of a chemical different polymer.     

Capabilities for Dielectric-Constant Gas Thermometry in a Special Large-Volume Liquid-Bath Thermostat

Dielectric-constant gas thermometry is being further developed at PTB to measure thermodynamic temperature and the Boltzmann constant at the triple point of water. For this purpose, a huge liquid-bath thermostat with a liquid volume of about 800 L has been built to provide a suitable thermal environment in the central working volume (diameter 0.5 m, height 0.65 m), in which the vacuum chamber containing the measuring system is placed. Measurements of the temperature field in the working volume have been performed with and without the chamber using a mesh of 12 platinum resistance thermometers at appropriate positions. The results verify that the temperature inhomogeneity in the bath is well below 1 mK as necessary. The uncertainty of the temperature measurement inside the measuring system must be of the order of 0.1 mK. Its thermal conditions have been, therefore, investigated in detail, too. Special emphasis was given to the thermalization after temperature changes.