Characterization of translucent segments observed in an smbA mutant of Escherichia coli

Abstract The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22°C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrastt microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22°C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.     

Chromosomal genes essential for stable maintenance of the mini-F plasmid in Escherichia coli

We have isolated mutants of Escherichia coli which do not support stable maintenance of mini-F plasmids (delta ccd rep+ sop+). These host mutations, named hop, were classified into five linkage groups on the E. coli chromosome. Genetic analyses of these hop mutations by Hfr mating and P1 transduction showed their loci on the E. coli genetic map to be as follows: hopA in the gyrB-tnaA region, hopB in the bglB-oriC region, hopD between 8 and 15 min, and hopE in the argA-thyA region. Kinetics of stability of the sop+ and delta sop mini-F plasmids in these hop mutants suggest that the hopA mutants are defective in partitioning of mini-F rather than in plasmid replication. The hopB, hopC, and hopD mutants were partially defective in replication of mini-F. The physical structure of the plasmid DNA was normal in hopA, B, C, and D mutants. Large amounts of linear multimers of plasmid DNA accumulated in mutants of the fifth linkage group (hopE). None of the hop mutations in any linkage group affected the normal growth of cells.     

Cloning of cDNA encoding human H-protein, a constituent of the glycine cleavage system

A cDNA that encodes human H-protein, a constituent protein of the glycine cleavage system, was cloned with anti-rat H-protein antibody as a probe from a human liver cDNA library constructed with an expression vector, lambda gt11. The longest size of cDNA of the isolated clones was about 750 base long (lambda HH15B9). On the other hand, we determined the primary structure of human H-protein from the amino terminal Ser by the 12th Val, including a hexapeptide, -Glu-Lys-His-Glu-Trp-Val-. In addition to the finding that most cDNA inserts cloned hybridized with the synthetic DNA probe composed of the possible sequences for the hexapeptide, we confirmed that lambda HH15B9 encodes the partial primary structure of H-protein in an open reading frame.     

New killing system controlled by two genes located immediately upstream of the mukB gene in Escherichia coli

The nucleotide sequence was determined of the region upstream of the mukB gene of Escherichia coli. Two new genes were found, designated kicA and kicB (killing of cell); the gene order is kicB-kicA-mukB. Promoter activities were detected in the regions immediately upstream of kicB and kicA, but not in front of mukB. Gene disruption experiments revealed that the kicA disruptant was nonviable, but the kicB-disrupted mutant and the mutant lacking both the kicB and kicA genes were able to grow. When kicA disruptant cells bearing a temperature-sensitive replication plasmid carrying the kicA ⁺ gene were grown at 30° C and then transferred to 42° C, the mutant cells gradually lost colony-forming ability, even in the presence of a mukB ⁺ plasmid. Rates of protein synthesis, but not of RNA or DNA synthesis, fell dramatically during incubation at 42° C. These results suggested that the kicB gene encodes a killing factor and the kicA gene codes for a protein that suppresses the killing function of the kicB gene product. It was also demonstrated that KicA and KicB can function as a post-segregational killing system, when the genes are transferred from the E. coli chromosome onto a plasmid.     

Seasonal variation of nitrification along a salinity gradient in an urban estuary

A review on salinity adaptation of marine molluscsbased on mainly Russian scientific literature ispresented. The existence of two relativelyindependent systems of adaptation to extreme(resistance level) and moderate (tolerance level)changes of environmental salinity was shown. Theresistance of molluscs is based mainly on an impededwater-salt exchange with the external medium due tomantle cavity hermetization. The tolerance ofmolluscs is determined by cellular mechanisms ofadaptation. Reversible changes of protein and RNAsynthesis, alteration of the pattern of multiplemolecular forms of different enzymes, and theregulation of ionic content and cell volume wereshown to be of importance for the above mentionedmechanisms. The efficiency of resistance andtolerance adaptations to salinity changes may varyin different species and in different colourphenotypes of the same species (intrapopulationalpolymorphism). Parasites (trematodes) may suppressthe resistance of the mollusc-host to extremesalinity changes without effecting the host'scapacity for adaptive changes in salinitytolerance.     

An improved method for labeling carboxyatractyloside by [3H]KBH4

Carboxyatractyloside was labeled with [3H]KBH4 after oxidation of the primary alcohol of the glucose disulfate moiety by dicyclohexylcarbodiimide and P2O5 under anhydrous conditions in a dimethylsulfoxide medium. The 3H-labeled product was purified by DE 52 column chromatography followed by Cellulofine GCL 25 column chromatography. The final 3H-labeled product gave a single spot on a thin-layer chromatogram, and its Rf value was the same as that of authentic carboxyatractyloside. The biological activities (such as inhibition of state 3 respiration and binding to the adenine nucleotide carrier) were also comparable with those of authentic carboxyatractyloside.     

Reduction of the level of the glycine cleavage system in the rat liver resulting from administration of dipropylacetic acid: an experimental approach to hyperglycinemia.

Prolonged administration of dipropylacetic acid, a branched-chain fatty acid, reduced the glycine cleavage activity in the liver of rat to about one-third of the activity in the control rat. The reduction of the activity appeared to be due mainly to reduction of the level of P-protein, a pyridoxal phosphate enzyme, which is responsible for the first step of the glycine cleavage, although dipropylacetic acid was also found to inhibit the activity of P-protein in vitro in a noncompetitive but partially competitive manner with respect to glycine. The rat treated with dipropylacetic acid may provide an experimental approach for the biochemical study of hyperglycinemia which accompanies to metabolic disorders of branchedchain keto acids. In the dipropylacetic acid-treated rat, however, the glycine concentration in the serum was not appreciably elevated and this may be accounted for by the fact that the activities of both the glycine cleavage system and serine dehydratase are considerably higher in the rat liver as compared with those in other animals including human.