Edwards R, Merrick M
Nitrogen Fixation Laboratory, University of Sussex, Brighton, UK.
Mol Gen Genet. 1995 Apr 20;247(2):189-98. doi: 10.1007/BF00705649.
The glnD gene in enteric bacteria encodes a uridylyltransferase/uridylyl-removing enzyme which acts as the primary nitrogen sensor in the nitrogen regulation (Ntr) system. We have investigated the role of this enzyme in transcriptional regulation of nitrogen fixation genes in Klebsiella pneumoniae by cloning glnD from this organism and constructing a null mutant by insertional inactivation of the chromosomal gene using the omega interposon. K. pneumoniae glnD encodes a 102.3 kDa polypeptide which is highly homologous to the predicted products of both Escherichia coli glnD and Azotobacter vinelandii nfrX. The glnD-omega mutant was unable to uridylylate PII and was altered in adenylylation/deadenylylation of glutamine synthetase. Uridylyltransferase was required for derepression of ntr-regulated promoters such as glnAp2 and pnifL but was not involved in the nif-specific response to changes in nitrogen status mediated by the nifL product. We conclude that a separate, as yet uncharacterised, nitrogen control system may be responsible for nitrogen sensing by NifL.
肠道细菌中的glnD基因编码一种尿苷酰转移酶/尿苷酰去除酶，它在氮调节（Ntr）系统中作为主要的氮传感器。我们通过从肺炎克雷伯菌中克隆glnD并使用ω插入子对染色体基因进行插入失活构建一个无效突变体，研究了该酶在肺炎克雷伯菌固氮基因转录调控中的作用。肺炎克雷伯菌glnD编码一个102.3 kDa的多肽，它与大肠杆菌glnD和棕色固氮菌nfrX的预测产物高度同源。glnD-ω突变体无法使PII尿苷酰化，并且谷氨酰胺合成酶的腺苷酰化/去腺苷酰化发生改变。尿苷酰转移酶是ntr调控启动子（如glnAp2和pnifL）去阻遏所必需的，但不参与由nifL产物介导的固氮特异性对氮状态变化的反应。我们得出结论，一个单独的、尚未被表征的氮控制系统可能负责NifL对氮的感应。
