Alvarez-Morales A, Dixon R, Merrick M
EMBO J. 1984 Mar;3(3):501-7. doi: 10.1002/j.1460-2075.1984.tb01837.x.
The nitrogen regulation system of Klebsiella pneumoniae comprises three genes ntrA, ntrB and ntrC. We have found that the glnA ntrBC regulon in K. pneumoniae has a similar structure, P1 glnA P2 ntrBC, to that in other enterobacteria. We have constructed plasmids with glnA and ntrB translational lacZ fusions and measured expression from P1 and/or P2 in a K. pneumoniae delta (glnA ntrBC) background with different plasmids which provided the ntrB, ntrC or nifA products in trans. These studies demonstrate that, as in other enterobacteria, transcription of ntrBC is from P1 under nitrogen deficiency and from P2 under nitrogen excess. The P1 promoter can be regulated both positively and negatively; activation requires both ntrB and ntrC products but the ntrC product is sufficient to repress. The P2 promoter is negatively controlled by the ntrC product. Comparison of the modes of regulation of P1 and P2 with regulation of the promoter of the nifLA operon leads us to suggest that these may represent three different classes of ntr-regulated promoters. Although previous studies have shown that the nifA product can substitute for the ntrC product as a positive activator of transcription for a number of promoters, we find that nifA product cannot substitute for ntrC product as a negative regulator at P1 or P2.
肺炎克雷伯菌的氮调节系统由三个基因ntrA、ntrB和ntrC组成。我们发现，肺炎克雷伯菌中的glnA ntrBC操纵子与其他肠杆菌中的结构相似，即P1 glnA P2 ntrBC。我们构建了带有glnA和ntrB翻译lacZ融合体的质粒，并在肺炎克雷伯菌δ（glnA ntrBC）背景下，用不同的质粒测量了P1和/或P2的表达，这些质粒在反式中提供了ntrB、ntrC或nifA产物。这些研究表明，与其他肠杆菌一样，ntrBC在氮缺乏时从P1转录，在氮过量时从P2转录。P1启动子可受到正调控和负调控；激活需要ntrB和ntrC产物，但ntrC产物足以起到抑制作用。P2启动子受ntrC产物的负调控。将P1和P2的调控模式与nifLA操纵子启动子的调控模式进行比较，使我们认为这些可能代表了三类不同的ntr调控启动子。尽管先前的研究表明，nifA产物可以替代ntrC产物作为许多启动子转录的正激活剂，但我们发现nifA产物不能替代ntrC产物在P1或P2处作为负调控因子。
