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91.
Genetic and molecular analysis of spontaneous respiratory deficient (res-) mutants of Escherichia coli K-12 总被引:2,自引:0,他引:2
L A Lewis K B Li A Gousse F Pereira N Pacheco S Pierre P Kodaman S Lawson 《Microbiology and immunology》1991,35(4):289-301
Respiratory deficient (res-) mutants of E. coli are slow growing microcolonial, anaerobic, catalase and benzidine negative strains whose broad phenotypic alteration may result from pleiotropic mutations in genes of the hemin biosynthetic pathway. They are easily recovered from platings of sensitive cells on concentrations of gentamicin higher than the minimal inhibitory concentration. These mutants show a dramatic change in their biochemical diagnostic profile resulting primarily from deficiencies in the active transport mechanisms of the cell. Using well-marked F- and Hfr strains, 157 mutants were analyzed from 3 different parent strains; all but 2 resulted from mutations in 3 loci of the hemin biosynthetic pathway. Of these a marked skew to hemB- mutations was seen, with more than 80% mapping there. The possibility that this hot spot resulted from transpositional activity was tested by Southern hybridization of EcoRI digests of the chromosomal DNA, using as a probe, a 2.8-kb fragment containing the hemB gene. The WT and other hemB+ control strains contained a 14.6-kb fragment. Of 18 hemB strains tested, 14 showed deletion and insertion mutations which fell into four classes based on the variation in the size of the fragment or on the absence of hybridization. The latter resulted from complete deletion of the hemB gene. An increase in fragment size from 1.5-kb to 3.4-kb was observed in some of the strains. 相似文献
92.
Polyethylene glycol precipitation for recovery of pathogenic viruses, including hepatitis A virus and human rotavirus, from oyster, water, and sediment samples. 总被引:11,自引:7,他引:4 下载免费PDF全文
Polyethylene glycol 6000 precipitation was found to be an effective concentration method that enhanced the chances for detecting human virus pathogens in environmental samples. Percent recoveries from eluates of fresh and estuarine waters with 8% polyethylene glycol 6000 averaged 86 for hepatitis A virus, 77 for human rotavirus Wa, 87 for simian rotavirus SA11, and 68 for poliovirus. Percent recoveries of 97, 40, 97 and 105, respectively, for the same viruses were obtained from oyster eluates by the same procedure. Percent recoveries of 97 for hepatitis A virus and 78 for human rotavirus Wa were obtained from sediment eluates containing 2 M NaNO3 with a final concentration of 15% polyethylene glycol 6000. The polyethylene glycol method was shown to be more effective than the organic flocculation method for recovery of hepatitis A virus and rotaviruses Wa and SA11, but not of poliovirus 1 in laboratory studies. In field trials, hepatitis A virus or rotavirus or both were recovered from 12 of 18 eluates by polyethylene glycol, compared with recovery from 9 of 18 eluates by organic flocculation from fresh and estuarine waters subject to pollution. 相似文献
93.
94.
Characterization of sodium transport in Acholeplasma laidlawii B cells and in lipid vesicles containing purified A. laidlawii (Na+-Mg2+)-ATPase by using nuclear magnetic resonance spectroscopy and 22Na tracer techniques. 下载免费PDF全文
S Mahajan R N Lewis R George B D Sykes R N McElhaney 《Journal of bacteriology》1988,170(12):5739-5746
The active transport of sodium ions in live Acholeplasma laidlawii B cells and in lipid vesicles containing the (Na+-Mg2+)-ATPase from the plasma membrane of this microorganism was studied by 23Na nuclear magnetic resonance spectroscopic and 22Na tracer techniques, respectively. In live A. laidlawii B cells, the transport of sodium was an active process in which metabolic energy was harnessed for the extrusion of sodium ions against a concentration gradient. The process was inhibited by low temperatures and by the formation of gel state lipid in the plasma membrane of this organism. In reconstituted proteoliposomes containing the purified (Na+-Mg2+)-ATPase, the hydrolysis of ATP was accompanied by the transport of sodium ions into the lipid vesicles, and the transport process was impaired by reagents known to inhibit ATPase activity. At the normal growth temperature (37 degrees C), this transport process required a maximum of 1 mol of ATP per mol of sodium ion transported. Together, these results provide direct experimental evidence that the (Na+-Mg2+)-ATPase of the Acholeplasma laidlawii B membrane is the cation pump which maintains the low levels of intracellular sodium characteristic of this microorganism. 相似文献
95.
D-serine dehydratase from Escherichia coli. DNA sequence and identification of catalytically inactive glycine to aspartic acid variants 总被引:3,自引:0,他引:3
M Marceau E McFall S D Lewis J A Shafer 《The Journal of biological chemistry》1988,263(32):16926-16933
We have identified two glycyl residues whose integrity is essential for the catalytic competence of a model pyridoxal 5'-phosphate requiring enzyme, D-serine dehydratase from Escherichia coli. This was accomplished by isolating and sequencing the structural gene from wild type E. coli and from two mutant strains that produce inactive D-serine dehydratase. DNA sequencing indicated the presence of a single glycine to aspartic acid replacement in each variant. The amino acid replacements lie in a glycine-rich region of D-serine dehydratase well removed from pyridoxal 5'-phosphate-binding lysine 118 in the primary structure of the enzyme. The striking effect of these two glycine to aspartic acid replacements on catalytic activity, the conservation of the glycine-rich region in several pyridoxal 5'-phosphate-dependent enzymes that catalyze alpha/beta-eliminations, and the placement of similar glycine-rich sequences in well-characterized active site structures suggest that the glycine-rich region interacts with the cofactor at the active site of the enzyme. 相似文献
96.
Intermolecular histone H4 interactions in core nucleosomes 总被引:1,自引:0,他引:1
Chicken histone H4, labeled at methionine-84 with 1-N-pyrenyliodoacetamide, has been incorporated into a nucleosome-like particle with core length DNA and unmodified histones H2A, H2B, and H3. These synthetic nucleosomes exhibit properties very similar to those displayed by native particles and those labeled with other fluors. The emission spectrum of the pyrene-labeled nucleosome was characteristic of excited dimer (excimer) fluorescence, indicating that the single pyrene groups on the two H4 molecules are in close proximity in the reconstituted particle. Histone H4 was also labeled randomly at lysines with a group that contains two pyrene moieties separated by 12 A at most. Incorporation of this histone into nucleosome-like particles provides an excimer standard which does not depend on intermolecular interactions. The properties of the pyrene-containing nucleosome were examined as a function of ionic strength. It was found that the H4-H4 pyrene excimer fluorescence exhibited a cooperative disruption centered at 0.1 M NaCl which preceded increases in accessibility and environment polarity revealed by other fluors attached at the same site. 相似文献
97.
DNA polymerase I is a multifaceted enzyme with one polymerizing and two exonuclease activities. Captan was previously shown to be an inhibitor of this enzyme's polymerizing activity and this report measures the effects of captan on the two exonuclease activities. When the holoenzyme was tested, captan enhanced the degradation of poly(dA-dT), T7 DNA and, to a significantly lesser extent, heat-denatured DNA. However, when the effects of captan were tested as a function of substrate concentration, the stimulatory influence was measured only at high substrate concentrations. At low concentrations of DNA, captan was inhibitory. Inhibition and enhancement each showed an ED50 of the same value (approx. 100 microM). By assaying the two exonuclease activities separately it was shown that the differential effect on the holoenzyme by captan was the result of a combined inhibition of the 3'----5' exonuclease and enhancement of the 5'----3' exonuclease. Klenow fragment with poly(dA-dT) as substrate was used to assay for 3'----5' exonuclease activity. Captan inhibited this exonuclease and the inhibition could be prevented by the addition of greater concentrations of substrate. Holoenzyme and poly(rA)-poly(dT) were used to assay for 5'----3' exonucleolysis, which was enhanced at higher concentrations of substrate in the presence of captan. 相似文献
98.
Primary structure of the chromosomal protein HMb from the archaebacteria Methanosarcina barkeri 总被引:3,自引:0,他引:3
B Laine F Chartier M Imbert R Lewis P Sautiere 《European journal of biochemistry》1986,161(3):681-687
The amino acid sequence of the protein HMb, a protein of 93 residues (Mr 10757) which represents the major acid-soluble component of the Methanosarcina barkeri nucleoprotein complex, has been established from automated sequence analysis of the protein and from structural data provided by peptides derived from cleavage of the protein at aspartic acid, arginine and methionine residues. The protein HMb is mainly characterized by a high amount of charged residues (15% of acidic residues and 26.8% of basic residues) which are distributed all along the polypeptide chain. The amino acid sequence of the protein HMb is not homologous to any eubacterial, archaebacterial or eukaryotic chromosomal proteins known up to now. 相似文献
99.
Clathrin (8 S) is known to polymerize into two varieties of basket structures (150 S or 300 S) under the normal buffer conditions [100 mM 2-(N-morpholino)ethanesulfonic acid (Mes), pH 5.9-6.7] used for the isolation of coated vesicles. However, it is now observed that under very low salt conditions (2 mM Mes, pH 5.9), it forms a homogeneous species with a sedimentation coefficient of 27 S. Increasing the salt concentration to 50 mM Mes completely converts all the 27S species into 150S baskets. Sedimentation equilibrium data show that this 27S species has a molecular weight that is 6 times that of the clathrin protomer and is the result of highly cooperative reversible self-association of the 8S protomer. Light-scattering studies show that the stabilities of 27S species and baskets (150 S or 300 S) are comparable. Fluorescent labeling of sulfhydryl groups with N-(1-anilinonaphthalenyl)maleimide indicates that the conformation of clathrin in 27S species and baskets (150 S or 300 S) is similar. Trypsin digestion reveals that in the 27S species clathrin has a conformation differing from that in both the 8S species and baskets. 相似文献
100.
Grazing by southern mullet, Liza richardsoni (Smith), on surf diatoms occurring in bloom concentrations off an ocean-exposed East Cape beach, South Africa, was investigated. Field observations and stomach content analysis demonstrated that surf diatoms taken from the air-water interface were a principal source of food. A qualitative examination of stomach contents revealed a feeding transition from planktonic carnivore in juveniles to a diet consisting entirely of surf diatoms in larger fishes. This change in diet commonly occurred at a standard length of 50–135 mm. Fish larger than 135 mm fed entirely on surf diatoms which were ingested together with large quantities of beach sediment. Grazing on surf diatoms only took place during daylight hours. Energy, ash, protein, fat and carbohydrate content determinations indicate a high food quality of surf diatoms. It is concluded that surf diatom accumulations form a richly concentrated and reliable food source of high nutritional quality for these fish. Possible widespread grazing on surf diatoms by mullets is considered. 相似文献