Toukdarian A, Kennedy C
EMBO J. 1986 Feb;5(2):399-407. doi: 10.1002/j.1460-2075.1986.tb04225.x.
The ntrA, ntrB and ntrC products are responsible for regulating the transcription of many genes involved in the assimilation of poor nitrogen sources in enteric bacteria. The presence of a similar system in the non-enteric bacterium Azotobacter vinelandii is reported here. Genes analogous to ntrA and ntrC were isolated from an A. vinelandii gene library by complementation of Escherichia coli mutants. The gene encoding glutamine synthetase, glnA, was also isolated and found to be adjacent to ntrC but distant from ntrA, as it is in enteric organisms. The cloned Azotobacter genes also complemented Klebsiella pneumoniae mutants and hybridized to K. pneumoniae ntrA, ntrC and glnA gene probes. The role of ntrA and ntrC in A. vinelandii was established by using Tn5 insertions in the cloned genes to construct mutants by marker exchange. These mutants show that both ntrA and ntrC are required for the utilization of nitrate as a nitrogen source. However, ntrC is not required for nitrogen fixation by A. vinelandii, in contrast with K. pneumoniae where both ntrA and ntrC are essential.
ntrA、ntrB和ntrC基因产物负责调控许多参与肠道细菌中贫氮源同化作用的基因的转录。本文报道了在非肠道细菌维涅兰德固氮菌中存在类似的系统。通过对大肠杆菌突变体进行互补，从维涅兰德固氮菌基因文库中分离出了与ntrA和ntrC类似的基因。编码谷氨酰胺合成酶的基因glnA也被分离出来，并且发现它与ntrC相邻，但与ntrA距离较远，就像在肠道生物中一样。克隆的固氮菌基因也能互补肺炎克雷伯菌突变体，并与肺炎克雷伯菌的ntrA、ntrC和glnA基因探针杂交。通过在克隆基因中使用Tn5插入来进行标记交换构建突变体，从而确定了ntrA和ntrC在维涅兰德固氮菌中的作用。这些突变体表明，利用硝酸盐作为氮源时，ntrA和ntrC都是必需的。然而，与ntrA和ntrC都必不可少的肺炎克雷伯菌不同，维涅兰德固氮菌进行固氮作用时不需要ntrC。
