Conservation of IS66 homologue of octopine Ti plasmid DNA in Rhizobium fredii plasmid DNA

Summary DNA sequences homologous to the T-DNA region of the octopine Ti plasmid from Agrobacterium tumefaciens are found in various fast-growing Rhizobium fredii strains. The largest fragment (BamHI fragment 2) at the right-boundary region of the core T-DNA hybridizes to more than one plasmid present in R. fredii. However, one smaller fragment (EcoRI fragment 19a) adjacent to the core T-DNA shows homology only with the plasmid carrying the symbiotic nitrogen-fixation genes (pSym). Hybridization data obtained with digested R. fredii USDA193 pSym DNA suggests that the homology is mainly with two HindIII fragments, 1.7 kb and 8.8 kb in size, of the plasmid. The 1.7 kb HindIII fragment also hybridizes to two regions of the virulence plasmid of A. tumefaciens, pAL1819, a deletion plasmid derived from the octopine Ti plasmid, pTiAch5. Hybridization studies with an insertion element IS66 from A. tumefaciens indicate that the 1.7 kb HindIII fragment of R. fredii plasmid, homologous to the T-DNA and the virulence region of Ti plasmid, is itself an IS66 homologue.     

水蒸汽蒸馏巴柑檬叶和果皮精油化学成分的研究

巴柑檬是我们第一次从国外引种成功的一种名贵香料植物。用色谱-质谱-计算机联用技术、毛细管气相色谱保留指数法和标准品叠加法分析了水蒸汽蒸馏巴柑檬叶和果皮精油的化学成分。从叶和果皮精油分离出来的220个和200个成分中,分别鉴定出48个和57个成分。鉴定组分的含量分别占叶和果皮精油的99.80％和98.54％。叶精油与果皮精油在化学成分方面的主要区别是叶油中萜烃化合物含量较低,而萜醇类化合物含量较高。     

Symbiotically defective histidine auxotrophs of Bradyrhizobium japonicum

Four histidine auxotrophs of Bradyrhizobium japonicum strain USDA 122 were isolated by random transposon Tn5 mutagenesis. These mutants arose from different, single transposition events as shown by the comparison of EcoRI and XhoI-generated Tn5 flanking sequences of genomic DNA. The mutants grew on minimal medium supplemented with l-histidine or l-histidinol but failed to grow with l-histidinol phosphate. While two of the muants were symbiotically defective and did not form nodules on Glycine max cvs. Lee and Peking and on Glycine soja, the other two mutants were symbiotically competent. Reversion to prototrophy occurred at a frequency of about 10^-7 on growth medium without added antibiotics, but prototrophs could not be isolated from growth medium containing 200 g/ml kanamycin and streptomycin. The prototrophic revertants formed nodules on all the soybean cultivars examined. When histidine was supplied to the plant growth medium, both nodulation deficient mutants formed effective symbioses. On histidine unamended plants, nodules were observed infrequently. Three classes of bacterial colonies were isolated from such infrequent nodules: class 1 were kanamycin resistant-auxotrophs; class 2 were kanamycin sensitive-prototrophs; and class 3 were kanamycin-sensitive auxotrophs. Our results suggest that two Tn5 insertion mutations in B. japonicum leading to histidine auxotrophy, affect nodulation in some way. These mutations are in regions that show no homology to the Rhizobium meliloti common nodulation genes.     

Polymorphic phase behaviour of dilinoleoylphosphatidylethanolamine and palmitoyloleoylphosphatidylcholine mixtures: Structural changes between hexagonal,cubic and bilayer phases

The polymorphic phase behaviour of dilinoleoylphosphatidyethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) is investigated by freeze-fracture electron microscopy, X-ray diffraction and ³¹P-NMR. The structures at 5% or less POPC are predominantly inverted hexagonal (H_II), whereas at 15% or more POPC, the structure is mostly bilayer (L), interrupted by defects (lipidic particles). A cubic phase structure is observed in the transition range between H and L phases; the cubic arrangement deteriorates at higher temperatures into an amorphous aggregate of spherical units. Both cubic and amorphous structures contribute to the isotropic ³¹P resonance, with no preference for PC or PE partitioning in the isotropic motion as observed by high resolution NMR. The existence of the cubic phase seems to depend critially on the homogeneity and the degree unsaturation of the phospholipids.     

Fluorescence and photoelectron studies of the intercalative binding of benz(a)anthracene metabolite models to DNA

An analog of the peptidyl transferase inhibitor sparsomycin was a competitive inhibitor (Ki = 1.8 microM) of peptidyl-puromycin synthesis on E. coli polysomes. Preincubation of polysomes with the compound enhanced the degree of inhibition of peptide bond formation. A model for the involvement of a histidine residue in peptidyl transferase activity is presented as a result of our observations which include direct association of [3H] labelled analog with 70S ribosomes. The correct oxidation state of sulfur in the compound was necessary for the "preincubation effect" and entry of the compound into bacterial cells.     

Purification and characterization of an enkephalin aminopeptidase from rat brain membranes

A membrane-bound aminopeptidase was purified from rat brain, and its activity was assayed by high-pressure liquid chromatography with Met-enkephalin as the substrate. The enzyme was extracted with 1% Triton X-100 and purified by chromatography, successively on DEAE-Sepharose CL-6B, Bio-Gel HTP, and Sephadex G-200 columns. The overall purification was about 1200-fold, with 25% yield. The purified enzyme showed one band on disc gel electrophoresis and two bands on sodium dodecyl sulfate electrophoresis with molecular weights of 62 000 and 66 000. The aminopeptidase has a pH optimum of 7.0, a Km of 0.28 mM, and a Vmax of 45 mumol (mg of protein)-1 min-1 for Met-enkephalin. It releases tyrosine from Met-enkephalin, but it does not split the byproduct. It does not hydrolyze gamma- or beta-endorphin, or dynorphin, but it does hydrolyze neutral and basic aminoacyl beta-naphthylamides. The enzyme is inhibited by the aminopeptidase inhibitors amastatin, bestatin, and bestatin-Gly. Its properties, such as its subcellular localization, substrate specificity, pH optimum, and molecular weight, distinguish it from leucine aminopeptidase, aminopeptidase A, aminopeptidase B, aminopeptidase M, and the soluble aminopeptidase for enkephalin degradation.     

Enhancement of lipid peroxidation in rat liver on acute exposure to styrene and acrylamide a consequence of glutathione depletion

Lipid peroxidation, glutathione level and activity of glutathione-S-transferase were studied in liver and brain of rats 4 and 3 h after a single i.p. administration of 0, 25, 75, 100 mg/kg acrylamide or 0, 50, 100, 200, 600 mg/kg styrene, respectively. In liver both acrylamide and styrene caused an increase in lipid peroxidation and decrease in glutathione contents and activity of glutathione-S-transferase in a dose dependent manner, while in brain only acrylamide produced a decrease in glutathione content. The decrease in glutathione content was not always associated with increase of lipid peroxidation. The enhancement of lipid peroxidation occurred only when glutathione contents were depleted to certain critical levels. No effect of acrylamide or styrene was seen on lipid peroxidation under in vitro conditions. The addition of glutathione in the incubation mixture significantly inhibited the rate of lipid peroxidation of liver homogenates of acrylamide and styrene treated animals.The results suggest that enhancement of lipid peroxidation in liver on exposure to acrylamide or styrene is a consequence of depletion of glutathione to certain critical levels. The inhibition of glutathione-S-transferase activity by acrylamide and styrene suggests that detoxication of these neurotoxic compounds could be suppressed following acute exposure.     

Lack of Chemically Induced Mutation in Repair-Deficient Mutants of Yeast

Two genes, rad6 and rad9, that confer radiation sensitivity in the yeast Saccharomyces cerevisiae also greatly reduce the frequency of chemically-induced reversions of a tester mutant cyc1-131, which is a chain initiation mutant in the structural gene determining iso-1-cytochrome c. Mutations induced by ethyl methanesulfonate (EMS), diethyl sulfate (DES), methyl methanesulfonate (MMS), dimethyl sulfate (DMS), nitroquinoline oxide (NQO), nitrosoguanidine (NTG), nitrogen mustard (HN2), beta-propiolactone, and tritiated uridine, as well as mutations induced by ultraviolet light (UV) and ionizing radiation were greatly diminished in strains homozygous for either the rad6 or rad9 gene. Nitrous acid and nitrosoimidazolidone (NIL), on the other hand, were highly mutagenic in these repair-deficient mutants, and at low doses, these mutagens acted with about the same efficiency as in the normal RAD strain. At high doses of either nitrous acid or NIL, however, reversion frequencies were significantly reduced in the two rad mutants compared to normal strains. Although both rad mutants are immutable to about the same extent, the rad9 strains tend to be less sensitive to the lethal effect of chemical mutagens than rad6 strains. It is concluded that yeast requires a functional repair system for mutation induction by chemical agents.     

Gene Differences between the Sex Ratio and Standard Gene Arrangements of the X Chromosome and Linkage Disequilibrium between Loci in the Standard Gene Arrangement of the X Chromosome in DROSOPHILA PSEUDOOBSCURA

The Standard and Sex Ratio gene arrangements of the X chromosome of D. pseudobscura differ from each other in allele frequencies at the four X chromosome loci, esterase-5, adult acid phosphatase-6, phosphoglucomutase-1 and octanol dehydrogenase-3. The Standard arrangement which is the common arrangement in all populations is polymorphic at these loci in varying degrees, the geographically less widespread Sex Ratio arrangement has little polymorphism and is genically predominantly E-5(1.04) AP-6(-) Pgm1(1.0) ODH-3(1.0). The Sex Ratio arrangement from different populations is alike at all of the four loci, the Standard arrangement shows some gene frequency differences among populations. The Standard and Sex Ratio arrangements differ from each other by three inversions which suggests that the two arrangements are "old". Gene differences between these two chromosome arrangements can be explained due to differential natural selection of alleles in the Standard and Sex Ratio arrangments.-The order and percent recombination among these four loci in the Standard arrangement are: E-5-.294-AP-6-.335-Pgm-1-.024-ODH-3. The Standard X chromosomes from four different wild populations were analyzed for evidence of linkage disequilibrium between pairs of loci at these four loci. No evidence of linkage disequilibrium between pairs of loci was obtained. However, when linkages involving simultaneously three loci, E-5, AP-6 and Pgm-1 are considered, then significant departure from linkage equilibrium is observed.     

Association of Alleles of the Malic Dehydrogenase Locus with a Pericentric Inversion in DROSOPHILA ROBUSTA

Associations of Malic dehydrogenase alleles with the third chromosome arrangement 3R and the pericentric arrangement 3L-R are described. Even though significant associations between alleles and inversions exist within a population, there is an overall similarity in MDH allele frequencies in different populations inspite of large differences in inversion frequencies.