The arcB gene of Escherichia coli encodes a sensor-regulator protein for anaerobic repression of the arc modulon

The arcA (dye) and arcB genes of Escherichia coli are responsible for anaerobic repression of target operons and regulons of aerobic function (the arc modulon). The amino acid sequence of ArcA (Dye) indicated that it is the regulator protein of a two-component control system. Here we show that ArcB is a membrane sensor protein on the basis of its deduced amino acid sequence (778 residues), hydropathicity profile, and cellular distribution. On the carboxyl end of the ArcB sequence there is an additional domain showing homology with conserved regions of regulator proteins. Deletion into this domain destroyed ArcB function. ArcB conserved a histidine residue for autophosphorylation of the sensor proteins, and aspartic residues important for the regulator proteins.     

The primary structure of the operons coding for Shigella dysenteriae toxin and temperature phage H30 shiga-like toxin

Nucleotide(nt) sequences were determined for the toxin (SHT) operon present in the chromosome of Shigella dysenteriae 1 and for the shiga-like toxin (SLT) operon found in the lambdoid phage H30 genome. The coding sequences of the sht and slt genes differ in 4 nt with 1 nt change responsible for an amino acid replacement. The deduced amino acid sequence in the A chain of the toxins is highly homologous to that of the A chain of ricin, a plant toxin. SHT-coding mRNAs were detected by mapping the 5' termini and using blot-hybridisation; one of them was more abundant and coded only for the B subunit of SHT while the other (bi-cistronic mRNA) encoded both subunits. An IS element related to the IS3 element of Escherichia coli was found in the chromosome of S. dysenteriae near the sht operon.     

Characterization and hydrodynamic behaviour of modified gelatin: I. Light scattering and viscometry studies

Commercial samples of gelatin modified by succinylation and currently used as plasma substitutes and fractionated samples obtained by diafiltration have been studied by viscometry, light scattering and osmometry. Viscometric results show that the aqueous medium containing potassium phosphate (0.1 ) and NaCl (0.12 ) at pH 3.3 behaves nearly like a theta solvent (a=0.48) for these modified gelatins. The Stockmayer-Fixman diagram reveals a negative slope attributed to a swelling of the macromolecules which decreases as the molecular weight _w increases. The Stokes radius R_H determined by quasielastic light scattering is independent of the pH of the medium in a range 7-3.3. The conformation of gelatins in solution has been characterized through the ratio _G· _H⁻¹, the radius of gyration _G being determined by viscometry. This ratio decreases as the molecular weight increases. The low molecular weight fractions have a more compact structure than the Gaussian chains in theta conditions. For high molecuar weight fractions, the values of _G· _H⁻¹ tend to those of an hard sphere.     

A Comparative Study of the Structures of {alpha}-Glucans from Suspension-Cultured Nonglutinous and Glutinous Rice Cells

-Glucans (average mol wt, 1.3 ? 10⁴) extracted with perchloricacid from 8-day-old suspension-cultured nonglutinous (var. Sasanishiki)and glutinous rice (var. Miyakogane) cells were compared. Theresults of hydrolysis by alpha;-, ß- and iso-amylasesand methylation analysis of the -glucans suggested that theirbasic structures are almost the same. These -glucans are highly-branchedpolysaccharides with an average chain length of about 9–10,with exterior and interior chain lengths of about 6–7and 2–3, respectively. ¹Current address: Laboratory of Food Science, Faculty of Education,Hirosaki University, Hirosaki, Aomori 036, Japan. (Received April 27, 1987; Accepted March 2, 1988)     

Formation of UDP-Xylose and Xyloglucan in Soybean Golgi Membranes

Soybean (Glycine max) membranes co-equilibrating with Golgi vesicles in linear sucrose gradients contained UDP-glucuronate carboxy-lyase and xyloglucan synthase activities. Digitonin solubilized and increased the activity of the membrane-bound UDP-glucuronate carboxy-lyase. UDP-xylose did not inhibit the transport of UDP-glucuronate into the lumen of Golgi vesicles but repressed the decarboxylation of the translocated UDP-glucuronate. The results suggest that UDP-glucuronate is transported into the vesicles by a specific carrier and decarboxylated to UDP-xylose within the lumen. On incubation of UDP-[¹⁴C]glucuronate with Golgi membranes in the presence of UDP-glucose, [¹⁴C]xylose-labeled xyloglucan was formed. Although the K_m value of UDP-glucuronate for the decarboxylation was 240 micromolar, the affinity of UDP-glucuronate for xyloglucan formation (31 micromolar) was similar to that of UDP-xylose (28 micromolar), suggesting a high turnover of UDP-xylose. The biosynthesis of UDP-xylose from UDP-glucuronate probably occurs in Golgi membranes, where xyloglucan subsequently forms from UDP-xylose and UDP-glucose.     

Intranuclear microinjection for transformation of tomato callus cells

An efficient method, called the culture plate method, was devised for microinjection of foreign materials into nuclei of tomato callus cells. The culture plate method, used in this study, is advantageous because cells suitable for microinjection can be selected microscopically and the injected cells subsequently cultured in the same plate. With this microinjection system, some foreign materials were injected into nuclei of callus cells without causing detrimental effects. Kanamycin-resistant callus clones were obtained 1 month after injection from single cells whose nuclei were microinjected with a NPT II DNA fragment of the pE2KX plasmid.     

Statistical analysis of nucleotide runs in coding and noncoding DNA sequences

A statistical analysis of the occurrence of particular nucleotide runs in DNA sequences of different species has been carried out. There are considerable differences of run distributions in DNA sequences of procaryotes, invertebrates and vertebrates. There is an abundance of short runs (1-2 nucleotides long) in the coding sequences and there is a deficiency of such runs in the noncoding regions. However, some interesting exceptions from this rule exist for the run distribution of adenine in procaryotes and for the arrangement of purine-pyrimidine runs in eucaryotes. The similarity in the distributions of such runs in the coding and noncoding regions may be due to some structural features of the DNA molecule as a whole. Runs of guanine (or cytosine) of three to six nucleotides occur predominantly in noncoding DNA regions in eucaryotes, especially in vertebrates.     

A selective inhibitor of thromboxane synthetase activity of rabbit heart tissue: a pyridazinic derivative

The effects of 2-(2 dimethylaminoethyl) 5-benzylidene 6-methyl (2H,4H)-3-pyridazinone (III) were studied on the biosynthesis of TXA2 and PGI2 in vitro the TXA2 and PGI2 synthetase activity of heart tissue. Biosyntheses of TXA2 and PGI2 were carried out using arachidonic acid as a substrate and horse platelet and aorta microsomes as sources of TXA2 and PGI2 synthetases respectively. TXB2 and 6-keto PGF1 alpha were determined by RIA. III--did not significantly modify either the biosynthesis of PGI2 in vitro or the PGI2 synthetase activity of heart tissue. did not significantly inhibit TXA2 biosynthesis in vitro but markedly reduced the TXA2 synthetase activity of heart tissue: for a microsomal fraction concentration of 100 micrograms protein, the ID50 was 6.37 X 10(-5) M +/- 1.29 X 10(-8) M. Thus III behaves as a specific inhibitor of the TXA2 synthetase activity of heart tissue and could have a beneficial use in therapeutics.