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This paper describes the role of nifA product on the ammonia regulation of nitrogen fixation in K. pneumoniae. A plasmid carrying nifA gene under the promoter of tetracycline resistance gene was constructed. When this nifA carrying plasmid was introduced into a glnAG mutant, the Nif~-phenotype of this gln mutant was suppressed. Furthermore, when the plasmid was introduced into the wild type and glnAG mutant, derepression of nitrogenase synthesis in ammonia occurred in both strains and the products of nif genes can be detected by two-dimensional gel electrophoresis in the extracts of these ammonia-grown bacterial cells.The constitutive synthesis of nitrogenase in NH_4~ was also demonstrated in free living nitrogen-fixing bacteria, Enterobacter cloacae, when the bacteria received the plasmid carrying nifA gent from K. pneumoniae. 相似文献
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本文叙述固氮基因nifA对肺炎克氏杆菌(Klebsiella pneumoniae)固氮作用的氨调节的影响。首先建构一个带有基因nifA的重组质粒,使基因nifA处于四环素抗性基因启动子控制之下。当这个建构成的带有基因nifA的质粒引入谷氨酰胺合成酶基因glnAG的突变型后,这个突变型的Nif~-表型就得到校正。此外,当这个质粒引入野生型和gln突变型后,两者在氨存在下都发生固氮酶合成的去阻遏作用,并在双向凝胶电泳上可以检测出固氮基因产物的存在。同样地,当自生固氮菌阴沟肠杆菌(Enterobacter cloacae)E26接受了这个重组质粒后也能观察到固氮酶的组成型合成。 相似文献
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When the R. meliloti (Rm) nifA'-lacZ fusion-carrying plasmids were introduced intothe strains of Agrobacterium tumefaciens, R. trifolii and R. astragalus, β-galactosidaseactivity was demonstrated. However, activity was not induced by microaerobiosis. Further-more, R. meliloti nifA'-lacZ fusion was also not expressed in the nodule bacteroids ofR. trifolii and R. astragalus. We speculate that some factor(s) important for the inductionof Rm nifA presumed to be the fixLJ regulatory system would not be operative in thesebacteria. Experiments using R. meliloti nifH'-lacZ/ K. Pneumoniae nifH'-lacZ fusion and theconstitutive Rm nifA system to test the nifA-dependent expression of nifH'-lacZ underaerobic and microaerobic conditions in E. coli were performed. The inhibition of the RmnifA activation of nifH'-lacZ expression in the bacteria grown in the aerobic conditionwas shown. Assays on the Rm nifA-m RNA produced by the constitutive Rm nifA in E.coli under aerobic and microaerobic conditions with the cloned ni 相似文献
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苜蓿根瘤菌(Rhizobium meliloti)nifA基因的异源表达及其产物的氧敏感性 总被引:2,自引:0,他引:2
当在土壤农杆菌、三叶草根瘤菌和紫云英根瘤菌中分别引入Rm nifA'-lacZ的质粒,可以测得β-gal活力,但其活力不受微氧诱导。当带有Rm nifA'-lacZ的三叶草根瘤菌和紫云英根瘤菌处于共生状态,β-gal的活力也无明显提高。推测苜蓿根瘤菌 nifA的诱导激活是受某些因子如fixLJ的专一作用。以大肠杆菌为材料在有氧和微氧下观察nifH'-lacZ受nifA的激活表达。RmnifA在有氧下不能激活Rm nifH'-lacZ和KpnifH'-lacZ的表达。同时证实RmnifA的mRNA在有氧下含量显著减少。 相似文献
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