Cannon M, Hill S, Kavanaugh E, Cannon F
Mol Gen Genet. 1985;198(2):198-206. doi: 10.1007/BF00382996.
A comprehensive study of nif expression in Klebsiella pneumoniae at the level of transcription, translation and nitrogenase activity during derepression and repression by NH+4 and O2 revealed that (1) transcription and translation rates remained coupled under all conditions; (2) these rates reached a peak during derepression and then decreased to a low level; (3) the transcription profile of nifLA had two peaks; the first was at 1 h before and the second coincided with that of the other operons; and (4) the peaks of nif transcription coincided with a trough in the profile of stringent regulation of RNA synthesis. Our results provide strong evidence that nif-specific repression by NH+4 and O2 occurs exclusively by transcription inhibition and that repression by O2 is independent of transcriptional regulation of the nifLA operon. We have also found evidence which together with the results of previous work shows that O2 repression of nifA mediated transcription involves the nifL gene product.
在肺炎克雷伯菌中，对nif基因在去阻遏以及被NH₄⁺和O₂阻遏过程中转录、翻译水平和固氮酶活性进行的一项全面研究表明：（1）在所有条件下转录和翻译速率保持耦合；（2）这些速率在去阻遏期间达到峰值，然后降至低水平；（3）nifLA的转录图谱有两个峰值，第一个在其他操纵子峰值前1小时，第二个与其他操纵子的峰值重合；（4）nif转录的峰值与RNA合成严格调控图谱中的低谷重合。我们的结果提供了有力证据，表明NH₄⁺和O₂对nif的特异性阻遏仅通过转录抑制发生，并且O₂的阻遏独立于nifLA操纵子的转录调控。我们还发现了一些证据，与之前的研究结果一起表明，O₂对nifA介导转录的阻遏涉及nifL基因产物。
