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141.
Nitrogen fixation ability of exopolysaccharide synthesis mutants of Rhizobium sp. strain NGR234 and Rhizobium trifolii is restored by the addition of homologous exopolysaccharides. 总被引:20,自引:12,他引:8
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Several transposon Tn5-induced mutants of the broad-host-range Rhizobium sp. strain NGR234 produce little or no detectable acidic exopolysaccharide (EPS) and are unable to induce nitrogen-fixing nodules on Leucaena leucocephala var. Peru or siratro plants. The ability of these Exo- mutants to induce functioning nodules on Leucaena plants was restored by coinoculation with a Sym plasmid-cured (Nod- Exo+) derivative of parent strain NGR234, purified EPS from the parent strain, or the oligosaccharide from the EPS. Coinoculation with EPS or related oligosaccharide also resulted in formation of nitrogen-fixing nodules on siratro plants. In addition, an Exo- mutant (ANU437) of Rhizobium trifolii ANU794 was able to form nitrogen-fixing nodules on white clover in the presence of added EPS or related oligosaccharide from R. trifolii ANU843. These results demonstrate that the absence of Rhizobium EPSs can result in failure of effective symbiosis with both temperate and subtropical legumes. 相似文献
142.
Regulation of two nickel-requiring (inducible and constitutive) hydrogenases and their coupling to nitrogenase in Methylosinus trichosporium OB3b. 总被引:4,自引:3,他引:1
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Two uptake hydrogenases were found in the obligate methanotroph Methylosinus trichosporium OB3b; one was constitutive, and a second was induced by H2. Both hydrogenases could be assayed by measuring methylene blue reduction anaerobically or by coupling their activity to nitrogenase acetylene reduction activity in vivo in an O2-dependent reaction. The H2 concentration for half-maximal activity of the inducible and constitutive hydrogenases in both assays was 0.01 and 0.5 bar (1 and 50 kPa), respectively, making it easy to distinguish these enzymes from one another both in vivo and in vitro. Hydrogen uptake was shown to be coupled to ATP synthesis in methane-starved cells. Methane, methanol, formate, succinate, and glucose all repressed the H2-mediated synthesis of the inducible hydrogenase. Furthermore, this enzyme was only expressed in N-starved cultures and was repressed by NH4+ and NO3-; synthesis of the constitutive hydrogenase was not affected by excess N in the growth medium. In nickel-free, EDTA-containing medium, the activities of these two enzymes were negligible; however, both enzyme activities appeared rapidly following the addition of nickel to the culture. Chloramphenicol, when added along with nickel, had no effect on the rapid appearance of either the constitutive or inducible activity, indicating that nickel is not required for synthesis of the hydrogenase apoproteins. These observations all suggest that these hydrogenases are nickel-containing enzymes. Finally, both hydrogenases were soluble and could be fractionated by 20% ammonium sulfate; the constitutive enzyme remained in the supernatant solution, while the inducible enzyme was precipitated under these conditions. 相似文献
143.
NAD-linked aldehyde dehydrogenase for aerobic utilization of L-fucose and L-rhamnose by Escherichia coli. 总被引:7,自引:6,他引:1
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Mutant analysis revealed that complete utilization of L-fucose and L-rhamnose by Escherichia coli requires the activity of a common NAD-linked aldehyde dehydrogenase which converts L-lactaldehyde to L-lactate. Mutations affecting this activity mapped to the ald locus at min 31, well apart from the fuc genes (min 60) encoding the trunk pathway for L-fucose dissimilation (as well as L-1,2-propanediol oxidoreductase) and the rha genes (min 88) encoding the trunk pathway for L-rhamnose dissimilation. Mutants that grow on L-1,2-propanediol as a carbon and energy source also depend on the ald gene product for the conversion of L-lactaldehyde to L-lactate. 相似文献
144.
The role of protein structure in the mitochondrial import pathway. Unfolding of mitochondrially bound precursors is required for membrane translocation 总被引:15,自引:0,他引:15
In order to examine the influence of protein structure on the post-translational import of a protein into mitochondria, the carboxyl-terminal 129 residues of F1-ATPase beta-subunit precursor (511aa) have been replaced with 61 residues of yeast copper metallothionein. Import of the F1 beta-copper metallothionein (beta CuMT) hybrid into mitochondria was as efficient as that of the F1 beta precursor in the absence of copper. Addition of copper to mitochondrial import reactions, which had no significant effect on import of the F1 beta-subunit precursor, blocked import of the beta CuMT protein. This copper-dependent transport block for the beta CuMT precursor occurred after the precursor was bound to mitochondria. Expression of the beta CuMT protein in vivo revealed that beta CuMT would bind copper and allow growth of a copper-sensitive yeast host on an otherwise inhibitory level of the cation as long as it was localized in the cytoplasm. These data indicate that the binding of copper by beta CuMT renders it refractile for partial unfolding which is necessary for its translocation into mitochondria. These observations provide an alternative scheme for the selection of mutants defective in mitochondrial import. 相似文献
145.
Protein translocation into Escherichia coli membrane vesicles is inhibited by functional synthetic signal peptides 总被引:7,自引:0,他引:7
A synthetic peptide corresponding to the signal sequence of wild type Escherichia coli lambda-receptor protein (LamB) inhibits in vitro translocation of precursors of both alkaline phosphatase and outer membrane protein A into E. coli membrane vesicles (half-maximal inhibition at 1-2 microM). By contrast, the inhibitory effect was nearly absent in a synthetic peptide corresponding to the signal sequence from a mutant strain that harbors a deletion mutation in the LamB signal region and displays an export-defective phenotype for this protein in vivo. Two peptides derived from pseudorevertant strains that arose from the deletion mutant and exported LamB in vivo were found to inhibit in vitro translocation with effectiveness that correlated with their in vivo export ability. Controls indicated that these synthetic signal peptides did not disrupt the E. coli membrane vesicles. These results can be interpreted to indicate that the presequences of exported proteins interact specifically with a receptor either in the E. coli inner membrane or in the cytoplasmic fraction. However, biophysical data for the family of signal peptides studied here reveal that they will spontaneously insert into a lipid membrane at concentrations comparable to those that cause inhibition. Hence, an indirect effect mediated by the lipid bilayer of the membrane must be considered. 相似文献
146.
The multidrug resistance gene PDR1 from Saccharomyces cerevisiae 总被引:18,自引:0,他引:18
E Balzi W Chen S Ulaszewski E Capieaux A Goffeau 《The Journal of biological chemistry》1987,262(35):16871-16879
147.
Identification of a possible nucleotide binding site in CheW, a protein required for sensory transduction in bacterial chemotaxis 总被引:13,自引:0,他引:13
CheW is an essential component of the system which mediates chemotaxis in Salmonella typhimurium and Escherichia coli. Here we report the nucleotide sequence of the cheW gene as well as the purification and characterization of the CheW protein. The DNA sequence predicts a protein of 18,000 molecular weight. The pure protein exhibits an apparent molecular weight of 18,000 during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Molecular sieve chromatography under nondenaturing conditions indicates a molecular weight of approximately 35,000, however. This result suggests that CheW is a homodimer. The predicted amino acid sequence between Thr-128 and Asp-160 fits a consensus exhibited by many proteins which bind purine nucleotides. 相似文献
148.
Y Suzuki C M Liu L P Chen D Ben-Nathan E F Wheelock 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(9):3146-3152
L5178Y lymphoma cells are restrained from progressive growth in peritoneal cell ("in vitro tumor-regressor" PC) cultures prepared from many DBA/2 mice which harbor the tumor cells in the peritoneal cavity in a tumor-dormant state. Treatment of these PC cultures with 'antibodies to murine interferon-gamma (MuIFN-gamma) and murine tumor necrosis factor (MuTNF) but not with antibody to interleukin 2 (IL-2) receptors eliminated the restraint on tumor cell growth and permitted their progressive proliferation. L5178Y cells were found to be resistant to the direct toxic effects of large concentrations (3,000 U/ml) of MuIFN-gamma and of MuTNF, either alone or in combination. Treatment of PC cultures from tumor-dormant mice, in which tumor cells grew progressively ("in vitro tumor-progressor"), but not PC cultures from normal mice, with exogenous MuIFN-gamma resulted in a marked inhibition of tumor cell growth. The MuIFN-gamma-induced cytotoxic activity was cell-mediated since no soluble tumor-cytotoxic factors could be detected in the cultures. MuIFN-gamma induced cytotoxic activity in plastic-adherent peritoneal cell (AD-PC) cultures, but induced no cytotoxic activity in nonadherent-PC cultures unless small numbers (2%) of AD-PC were present, and inclusion of antibody to MuTNF in these mixed PC cultures blocked the development of cytotoxic activity. Antibody to MuTNF also blocked the development of cytotoxic activity in cultures of MuIFN-gamma-treated whole PC and AD-PC from tumor-dormant mice. These results indicate that MuIFN-gamma and MuTNF are both important in restraining tumor cell growth in PC cultures from tumor-dormant mice, and that MuIFN-gamma requires the presence of MuTNF to induce cytotoxic activity in these cultures. 相似文献
149.
The androgen-dependent mouse seminal vesicle secretory protein IV: characterization and complementary deoxyribonucleic acid cloning 总被引:4,自引:0,他引:4
Y H Chen B T Pentecost J A McLachlan C T Teng 《Molecular endocrinology (Baltimore, Md.)》1987,1(10):707-716
Seminal vesicle secretory protein IV of a mouse has been isolated, and the cDNA coding for its mRNA has been cloned and sequenced. The 556-nucleotides encode 16 amino acid signal peptides and 92 residues of mature protein. Considerable homology between mouse and rat SVS IV cDNA was found. In the leader peptide and 3'-noncoding region there is 92% and 85% homology, respectively. The other regional homologies are 86% for the first 12, 68.5% for the last 35, and 40% for the middle 44 amino acids. The expression of mouse SVS IV mRNA is under the control of androgen. Administration of testosterone to castrated mice resulted in induction of the mRNA level to 50% of the mature male in 96 h of hormone treatment. Secretion of the protein after testosterone injection follows a similar pattern. 相似文献
150.
Classical Raman spectroscopic studies of NADH and NAD+ bound to liver alcohol dehydrogenase by difference techniques 总被引:1,自引:0,他引:1
We report the Raman spectra of reduced and oxidized nicotinamide adenine dinucleotide (NADH and NAD+, respectively) and adenosine 5'-diphosphate ribose (ADPR) when bound to the coenzyme site of liver alcohol dehydrogenase (LADH). The bound NADH spectrum is calculated by taking the classical Raman difference spectrum of the binary complex, LADH/NADH, with that of LADH. We have investigated how the bound NADH spectrum is affected when the ternary complexes with inhibitors are formed with dimethyl sulfoxide (Me2SO) or isobutyramide (IBA), i.e., LADH/NADH/Me2SO or LADH/NADH/IBA. Similarly, the difference spectra of LADH/NAD+/pyrazole or LADH/ADPR with LADH are calculated. The magnitude of these difference spectra is on the order of a few percent of the protein Raman spectrum. We report and discuss the experimental configuration and control procedures we use in reliably calculating such small difference signals. These sensitive difference techniques could be applied to a large number of problems where the classical Raman spectrum of a "small" molecule, like adenine, bound to the active site of a protein is of interest. The spectrum of bound ADPR allows an assignment of the bands of the bound NADH and NAD+ spectra to normal coordinates located primarily on either the nicotinamide or the adenine moiety. By comparing the spectra of the bound coenzymes with model compound data and through the use of deuterated compounds, we confirm and characterize how the adenine moiety is involved in coenzyme binding and discuss the validity of the suggestion that the adenine ring is protonated upon binding. The nicotinamide moiety of NADH shows significant molecular changes upon binding.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献