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排序方式: 共有174条查询结果,搜索用时 15 毫秒
1.
Chemotactic responses by motile bacteria 总被引:3,自引:0,他引:3
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Thymine glycol-DNA glycosylase/AP endonuclease of CEM-C1 lymphoblasts: a human analog of Escherichia coli endonuclease III 总被引:1,自引:0,他引:1
K Lee W H McCray P W Doetsch 《Biochemical and biophysical research communications》1987,149(1):93-101
A thymine glycol-DNA glycosylase/AP endonuclease has been identified in human CEM-C1 lymphoblasts. The enzyme is active in the absence of divalent cations and has an apparent molecular size of approximately 60,000 daltons. The enzyme releases thymine glycol from osmium tetroxide-damaged DNA via an N-glycosylase activity and is associated with an endonuclease activity that mediates phosphodiester bond cleavage at sites of thymine glycol and apurinic sites. We propose that this enzyme, which we call redoxyendonuclease, is the human analog of a bacterial enzyme, E. coli endonuclease III, that recognizes oxidative DNA damage. 相似文献
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Structural determination of the ultraviolet light-induced thymine-cytosine pyrimidine-pyrimidone (6-4) photoproduct. 总被引:12,自引:5,他引:7
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Ultraviolet light induces damage to DNA, with the majority of the damage expressed as the formation of cyclobutane dimers and pyrimidine-pyrimidone (6-4) photoproducts. The (6-4) photoproducts have been implicated as important UV light-induced premutagenic DNA lesions. The most abundant of the (6-4) products is the thymine-cytosine pyrimidine-pyrimidone (6-4) photoproduct, or TC (6-4) product. The structure of the TC (6-4) product was deduced by proton NMR, IR, and fast atom bombardment mass spectroscopy, and the product was found to differ from the previously described photoadduct, Thy(6-4)Pyo, by the presence of an amino group at the 5 position of the 5' pyrimidine. The implications of this structure on DNA base pairing and the induction of ultraviolet light-induced mutations are discussed. 相似文献
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Christina Kennedy Natalie Doetsch Dietmar Meletzus Eduardo Patriarca Mohamad Amar Maurizio Iaccarino 《Plant and Soil》1994,161(1):43-57
A plentiful supply of fixed nitrogen as ammonium (or other compounds such as nitrate or amino acids) inhibits nitrogen fixation in free-living bacteria by preventing nitrogenase synthesis and/or activity. Ammonium and nitrate have variable effects on the ability ofRhizobiaceae (Rhizobium, Bradyrhizobium andAzorhizobium) species to nodulate legume hosts and on nitrogen fixation capacity in bacteroid cells contained in nodules or in plant-free bacterial cultures. In addition to effects on nitrogen fixation, excess ammonium can inhibit activity or expression of other pathways for utilization of nitrogenous compounds such as nitrate (through nitrate and nitrite reductase), or glutamine synthetase (GS) for assimilation of ammonium. This paper describes the roles of two key genesglnB andglnD, whose gene products sense levels of fixed nitrogen and initiate a cascade of reactions in response to nitrogen status. While work onEscherichia coli and other enteric bacteria provides the model system,glnB and, to a lesser extent,glnD have been studied in several nitrogen fixing bacteria. Such reports will be reviewed here. Recent results on the identity and function of theglnB andglnD gene products inAzotobacter vinelandii (a free-living soil diazotroph) and inRhizobium leguminosarum biovarviciae, hereinafter designatedR.l. viciae will be presented. New data suggests thatAzotobacter vinelandii probably contains aglnB-like gene and this organism may have twoglnD-like genes (one of which was recently identified and namednfrX). In addition, evidence for uridylylation of theglnB gene product (the PII protein) ofR. l. viciae in response to fixed nitrogen deficiency is presented. Also, aglnB mutant ofR. l. viciae has been isolated; its characteristics with respect to expression of nitrogen regulated genes is described. 相似文献
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Single-strand-specific nucleases are a diverse and important group of enzymes that are able to cleave a variety of DNA structures present in duplex molecules. Nuclease SP, an enzyme from spinach, has been purified to apparent homogeneity, allowing for the unambiguous characterization of a number of its physical properties as well as its DNA strand cleavage specificities. The effects of ionic strength, pH, divalent metal cations, and temperature on nuclease SP activity have been examined in detail. Nuclease SP was found to be quite thermostable and could be stimulated by Co2+. In addition, the cleavage of UV-damaged and undamaged supercoiled plasmid substrates under a variety of conditions suggests that at least two types of structures are recognized and processed by nuclease SP: UV photoproduct-induced distortions and unwound "nuclease hypersensitive sites". These studies indicate that nuclease SP is functionally related to other single-strand-specific nucleases and is a potential enzymatic tool for probing and manipulating various types of DNA structures. 相似文献
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A method is described for obtaining a highly active proteolytic enzyme from aMicrosporum species. This protease was purified (200-fold) from a cell-free culture medium by concentration with Carbowax, ammonium sulfate fractionation, charcoal and Celite filtration, calcium phosphate gel treatment, and column chromatography. The pH and temperature optima are 6.8 and 35 C respectively. Requirement of one or more free sulfhydryl group(s) for enzyme activity was indicated by inhibition withp-chloromercuric benzoate. Ethylenediaminetetraacetic acid also caused inhibition of proteolytic activity, which suggests involvement of a metal ion. The enzyme appears to be most active in the reduced form;l-cysteine and 2,3 dimercapto-l-propanol doubled the rate of activity. It has an approximate molecular weight of 51,000 to 69,000. The enzyme was highly active on all proteins examined. 相似文献
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