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961.
Regulation of expression of glutamine synthetase in a symbiotic Nostoc strain associated with Anthoceros punctatus. 总被引:5,自引:3,他引:2 下载免费PDF全文
A characteristic of N2-fixing cyanobacteria in symbiotic associations appears to be release of N2-derived NH4+. The specific activity of the primary ammonium-assimilating enzyme, glutamine synthetase (GS), was found to be three- to fourfold lower in Nostoc sp. strain 7801 grown in symbiotic association with the bryophyte Anthoceros punctatus than in free-living Nostoc sp. strain 7801. Quantitative immunological assays with antisera against GS purified from Nostoc sp. strain 7801 and from Escherichia coli indicated that similar amounts of the GS protein were present in symbiotic (50 micrograms mg-1) and free-living (68 micrograms mg-1) cultures. The conclusion from these experiments is that GS is regulated by a posttranslational mechanism in Anthoceros-associated Nostoc sp. strain 7801. However, the results of comparative catalytic and immunological experiments between N2- and NH4+-grown free-living Nostoc sp. strain 7801 implied control of GS synthesis. A correlation was not observed between the level of GS expression and the extent of symbiotic heterocyst differentiation in Nostoc sp. strain 7801 associated with A. punctatus. 相似文献
962.
Transfer of phosphoethanolamine residues from phosphatidylethanolamine to the membrane-derived oligosaccharides of Escherichia coli. 总被引:2,自引:0,他引:2 下载免费PDF全文
The membrane-derived oligosaccharides (MDO) of Escherichia coli are periplasmic constituents composed of glucose residues linked by beta-1,2 and beta-1,6 glycosidic bonds. MDO are substituted with phosphoglycerol, phosphoethanolamine, and succinic acid moieties. The phosphoglycerol residues present on MDO are derived from phosphatidylglycerol (B. J. Jackson and E. P. Kennedy, J. Biol. Chem. 258:2394-2398, 1983), but evidence as to the source of the phosphoethanolamine residues has been lacking. We now report that phosphatidylethanolamine, exogenously added to intact cells of E. coli, provides a source of phosphoethanolamine residues that are transferred to MDO. The biosynthesis of phosphoethanolamine-labeled MDO is osmotically regulated, with maximum synthesis occurring during growth in medium of low osmolarity. 相似文献
963.
DNA replication by a DNA-membrane complex extracted from Bacillus subtilis: site of initiation in vitro and initiation potential of subcomplexes. 总被引:7,自引:4,他引:3 下载免费PDF全文
A DNA-membrane complex extracted from Bacillus subtilis was studied further as a model system for initiation of bacterial DNA replication in vitro. Of three subcomplexes purified from the crude complex by a combination of CsCl and sucrose gradient centrifugation, the synthetic capability of only one was inhibited significantly by streptovaricin, a known inhibitor of RNA primer formation. A selective enrichment in the level of this subcomplex was obtained by manipulating a thymine-requiring mutant. The synthetic capabilities of an enriched and nonenriched DNA-membrane complex were compared in the presence and absence of streptovaricin. Although the rate and extent of DNA synthesis per unit of protein were approximately the same in the absence of the antibiotic, there was a much greater inhibition of synthesis shown by the enriched complex in the presence of streptovaricin. Although the amount of DNA present in the putative initiation subcomplex was less than 0.3 to 0.4% of the total DNA present in the crude complex, such DNA, except for a few quantitative differences, was still representative of genomic DNA. Newly synthesized DNA hybridized to specific origin- and non-origin-derived restriction fragments of the B. subtilis genome. However, when an elongation inhibitor (ddCTP) was added, hybridization of such DNA to almost all of the nonorigin fragments disappeared or was reduced drastically, whereas origin region hybridization patterns remained strong. The highest level of hybridization in the origin region occurred with a BamHI (B7) restriction fragment of 5.6 kilobases that has been implicated by others as one site initiation in vivo (N. Ogasawara, M. Seiki, and H. Yoshikawa, Nature (London) 281:702-704, 1979; S. J. Seror-Laurent and G. Henckes, Proc. Natl. Acad. Sci. USA 82:3586-3590, 1985). 相似文献
964.
Involvement of both cellulose fibrils and a Ca2+-dependent adhesin in the attachment of Rhizobium leguminosarum to pea root hair tips. 总被引:19,自引:11,他引:8 下载免费PDF全文
We have previously described an assay for the attachment of Rhizobium bacteria to pea root hair tips (cap formation) which was used as a model to study the attachment step in the nodulation process. Under all conditions tested, a positive correlation was observed between the percentage of fibrillated cells and the ability of these bacteria to form caps and to adhere to glass, suggesting that fibrils play a role in the attachment of Rhizobium leguminosarum to pea root hair tips and to glass (G. Smit, J. W. Kijne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986). In the present paper the chemical and functional characterization of the fibrils of R. leguminosarum is described. Characterization of purified fibrils by infrared spectroscopy and cellulase treatment followed by thin-layer chromatography showed that the fibrils are composed of cellulose. Purified cellulose fibrils, as well as commercial cellulose, inhibited cap formation when present during the attachment assay. Incubation of the bacteria with purified cellulase just before the attachment assay strongly inhibited cap formation, indicating that the fibrils are directly involved in the attachment process. Tn5-induced fibril-overproducing mutants showed a greatly increased ability to form caps, whereas Tn5-induced fibril-negative mutants lost this ability. None of these Tn5 insertions appeared to be located on the Sym plasmid. Both types of mutants showed normal nodulation properties, indicating that cellulose fibrils are not a prerequisite for successful nodulation under the conditions used. The ability of the fibril-negative mutants to attach to glass was not affected by the mutations, indicating that attachment to pea root hair tips and attachment to glass are (partly) based on different mechanisms. However, growth of the rhizobia under low Ca2+ conditions strongly reduced attachment to glass and also prevented cap formation, although it had no negative effect on fibril synthesis. This phenomenon was found for several Rhizobium spp. It was concluded that both cellulose fibrils and a Ca2+ -dependent adhesin(s) are involved in the attachment of R. leguminosarum to pea root hair tips. A model cap formation as a two-step process is discussed. 相似文献
965.
We present the nucleotide sequence of the oriT region from plasmid R100. Comparison to other IncF plasmids revealed homology around the proposed nick sites as well as conservation of inverted repeated sequences in the nonhomologous region. Three areas showed strong homology (eight of nine nucleotides) to the consensus sequence for binding of integration host factor, suggesting a role for this DNA-binding protein in nicking at oriT. 相似文献
966.
Campylobacter pylori, the spiral bacterium associated with human gastritis, is not a true Campylobacter sp. 总被引:30,自引:10,他引:20 下载免费PDF全文
P J Romaniuk B Zoltowska T J Trust D J Lane G J Olsen N R Pace D A Stahl 《Journal of bacteriology》1987,169(5):2137-2141
Comparison of partial 16S rRNA sequences from representative Campylobacter species indicates that the Campylobacter species form a previously undescribed basic eubacterial group, which is related to the other major groups only by very deep branching. This analysis was extended to include the spiral bacterium associated with human gastritis, Campylobacter pylori (formerly Campylobacter pyloridis). The distance between C. pylori and the other Campylobacter species is sufficient to exclude the pyloric organism from the Campylobacter genus. The results indicate that C. pylori is more closely related to Wolinella succinogenes than it is to the other Campylobacter species inspected. Another close relative of the campylobacters was found to be Thiovulum, a sulfide-dependent marine bacterium. 相似文献
967.
Comparative organization of nitrogen fixation-specific genes from Azotobacter vinelandii and Klebsiella pneumoniae: DNA sequence of the nifUSV genes. 总被引:10,自引:8,他引:2 下载免费PDF全文
J Beynon A Ally M Cannon F Cannon M Jacobson V Cash D Dean 《Journal of bacteriology》1987,169(9):4024-4029
In the facultative anaerobe Klebsiella pneumoniae 17 nitrogen fixation-specific genes (nif genes) have been identified. Homologs to 12 of these genes have now been isolated from the aerobic diazotroph Azotobacter vinelandii. Comparative studies have indicated that these diverse microorganisms share striking similarities in the genetic organization of their nif genes and in the primary structure of their individual nif gene products. In this study the complete nucleotide sequence of the nifUSV gene clusters from both K. pneumoniae and A. vinelandii were determined. These genes are identically organized on their respective genomes, and the individual genes and their products exhibit a high degree of interspecies sequence homology. 相似文献
968.
Specificity of mutation by UV light and delayed photoreversal in umuC-defective Escherichia coli K-12: a targeting intermediate at pyrimidine dimers. 总被引:1,自引:1,他引:0 下载免费PDF全文
Prototrophic mutants produced by UV light in Escherichia coli K-12 strains with argE3(Oc) and hisG4(Oc) defects are distinguished as backmutations and specific nonsense suppressor mutations. In strains carrying a umuC defect, mutants are not produced unless irradiated cells are incubated and then exposed to photoreversing light (delayed photoreversal mutagenesis). The mutants thus produced are found to be specifically suppressor mutations and not backmutations. The suppressor mutations are primarily glutamine tRNA ochre suppressor mutations, which have been attributed previously to mutation targeted at T = C pyrimidine dimers. In a lexA51 recA441 strain, where the SOS mutagenesis functions are constitutive, targeting at dimers is confirmed by demonstrating that the induction of glutamine tRNA suppressor mutations is susceptible to photoreversal. In the same strain induction of backmutations is not susceptible to photoreversal. Thus delayed photoreversal mutagenesis produces suppressor mutations that can be targeted at pyrimidine dimers and does not produce backmutations that are not targeted at pyrimidine dimers. This correlation supports the idea that delayed photoreversal mutagenesis in umuC defective cells reflects a mutation process arrested at a targeting pyrimidine dimer photoproduct, which is the immediate cause of both the alteration in DNA sequence and the obstruction (unless repaired) to mutation fixation and ultimate expression. 相似文献
969.
970.
Cloning and expression in Escherichia coli of three fragments of diphtheria toxin truncated within fragment B. 总被引:5,自引:3,他引:2 下载免费PDF全文
We have constructed three different truncated versions of diphtheria toxin (a 535-amino-acid polypeptide) which correspond to the N-terminal 290, 377, and 485 amino acids of the toxin. These lengths include one, three, and all four of the putative membrane-spanning sequences of the toxin which are thought to play a role in the translocation of fragment A into cells. Each of these three genes has been modified at its 3' end to code for a C-terminal cysteine (to allow for disulfide linkage of a targeting ligand) or a gene fusion with alpha-melanocyte-stimulating hormone. We have also substituted the native diphtheria tox promoter (ptox) with the lambda pR promoter in an effort to overexpress these proteins. The truncated genes are expressed in Escherichia coli from both the tox promoter in a constitutive fashion and from the pR promoter by using the heat-inducible cI857 repressor. The clones produce proteins which react with anti-diphtheria toxin serum, which migrate at the anticipated Mr on Western blots, and which have ADP-ribosyltransferase activity. Constitutive synthesis from ptox leads to severe proteolytic degradation even in a protease-deficient strain. High-level expression from the pR promoter in the same lon htpR strain allows the full-length polypeptides to accumulate but also stops the growth of the cells. It appears that removal of as few as 50 amino acids from the C-terminus of diphtheria toxin alters its conformation, making it a target for proteases and causing overexpression lethality in the host cells. 相似文献