Inoue A, Shigematsu T, Hidaka M, Masaki H, Uozumi T
Department of Biotechnology, University of Tokyo, Japan.
Gene. 1996 Apr 17;170(1):101-6. doi: 10.1016/0378-1119(95)00852-7.
From Azospirillum lipoferum (Al) FS, a nitrogen-fixing bacterium isolated from the rhizosphere of rice, we cloned and sequenced draT, encoding dinitrogenase reductase ADP-ribosyltransferase, and draG, encoding dinitrogenase reductase-activating glycohydrolase. The nucleotide sequences of draTG showed extensive similarity to the same genes from Azospirillum brasilense, Rhodospirillum rubrum and Rhodobacter capsulatus, and they are assumed to be co-transcribed as a single operon. When this draTG operon was introduced into Klebsiella oxytoca, this organism acquired the ability to respond to extracellular NH(+4) ions with reversible inhibition of nitrogenase activity, similar to that seen in Al FS. We constructed a plasmid containing a draT::lacZ gene fusion and found that beta-galactosidase activity was detected under microaerobic conditions, regardless of NH(+4) concentration, but not under aerobic conditions. This indicates that the transcription of draTG responds to the level of oxygen, but not to that of NH(+4) ions.
从从水稻根际分离出的固氮细菌脂环酸芽孢杆菌（Al）FS中，我们克隆并测序了编码固氮酶还原酶ADP-核糖基转移酶的draT和编码固氮酶还原酶激活糖水解酶的draG。draTG的核苷酸序列与来自巴西固氮螺菌、深红红螺菌和荚膜红细菌的相同基因具有广泛的相似性，并且它们被认为作为一个单一操纵子共同转录。当这个draTG操纵子被导入产酸克雷伯菌时，该生物体获得了对细胞外NH₄⁺离子作出反应并可逆抑制固氮酶活性的能力，类似于在Al FS中观察到的情况。我们构建了一个含有draT::lacZ基因融合体的质粒，发现无论NH₄⁺浓度如何，在微需氧条件下都能检测到β-半乳糖苷酶活性，但在好氧条件下则检测不到。这表明draTG的转录对氧水平有反应，而对NH₄⁺离子水平没有反应。
