TRANSCRIPTIONAL ACTIVATION OF THE NITROGENASE PROMOTER IN-VITRO - ADENOSINE NUCLEOTIDES ARE REQUIRED FOR INHIBITION OF NIFA ACTIVITY BY NIFL
TRANSCRIPTIONAL ACTIVATION OF THE NITROGENASE PROMOTER IN-VITRO - ADENOSINE NUCLEOTIDES ARE REQUIRED FOR INHIBITION OF NIFA ACTIVITY BY NIFL
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DOI：
10.1128/jb.177.5.1186-1195.1995
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发表时间：
1995-03-01
影响因子：
3.2
通讯作者：
DIXON, R
中科院分区：
文献类型：
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作者：
EYDMANN, T;SODERBACK, E;DIXON, R
增强子结合蛋白NIFA是通过另一种全酶形式的RNA聚合酶转录激活nif启动子所必需的，该RNA聚合酶含有sigma因子sigma(54)(sigma(N))。NIFA水解三磷酸核苷，催化闭合启动子复合体异构化为转录活性开放复合体。在体内，NIFA的活性被氧和固定氮反应的调节蛋白NIFL所拮抗。我们研究了NIFA在开放启动子复合体的形成和稳定性中对核苷酸的需求，以及NIFL在肺炎克雷伯菌nifH启动子上对其活性的抑制。含有Sigma(54)的RNA聚合酶形成的开放复合体在GTP存在下比在ATP存在下对肝素挑战的稳定性要高得多。这种差异稳定性很可能是由于GTP是该启动子上的起始核苷酸所致。棕色固氮菌NIFL抑制天然NIFA开放复合体的形成需要特异性的腺苷核苷，在此条件下NIFA的核苷三磷酸酶活性被NIFL强烈抑制。我们提出了一个模型，其中NIFL通过腺苷核苷酸开关来调节NIFA的活性。
The enhancer-binding protein NIFA is required for transcriptional activation of nif promoters by the alternative holoenzyme form of RNA polymerase, which contains the sigma factor sigma(54) (sigma(N)). NIFA hydrolyzes nucleoside triphosphates to catalyze the isomerization of closed promoter complexes to transcriptionally competent open complexes. The activity of NIFA is antagonized by the regulatory protein NIFL in response to oxygen and fixed nitrogen in vivo. We have investigated the requirement for nucleotides in the formation and stability of open promoter complexes by NIFA and inhibition of its activity by NIFL at the Klebsiella pneumoniae nifH promoter. Open complexes formed by sigma(54)-containing RNA polymerase are considerably more stable to heparin challenge in the presence of GTP than in the presence of ATP. This differential stability is most probably a consequence of GTP being the initiating nucleotide at this promoter. Adenosine nucleosides are specifically required for Azotobacter vinelandii NIFL to inhibit open complex formation by native NIFA, and the nucleoside triphosphatase activity of NIFA is strongly inhibited by NIFL under these conditions. We propose a model in which NIFL modulates the activity of NIFA via an adenosine nucleotide switch.