Kessler P S, Leigh J A
Department of Microbiology, University of Washington, Seattle, Washington 98195, USA.
Genetics. 1999 Aug;152(4):1343-51. doi: 10.1093/genetics/152.4.1343.
We have used genetic methods in Methanococcus maripaludis to study nitrogen metabolism and its regulation. We present evidence for a "nitrogen regulon" in Methanococcus and Methanobacterium species containing genes of nitrogen metabolism that are regulated coordinately at the transcriptional level via a common repressor binding site sequence, or operator. The implied mechanism for regulation resembles the general bacterial paradigm for repression, but contrasts with well-known mechanisms of nitrogen regulation in bacteria, which occur by activation. Genes in the nitrogen regulons include those for nitrogen fixation, glutamine synthetase, (methyl)ammonia transport, the regulatory protein GlnB, and ammonia-dependent NAD synthetase, as well as a gene of unknown function. We also studied the function of two novel GlnB homologues that are encoded within the nif gene cluster of diazotrophic methanogens. The phenotype resulting from a glnB null mutation in M. maripaludis provides direct evidence that glnB-like genes are involved in "ammonia switch-off," the post-transcriptional inhibition of nitrogen fixation upon addition of ammonia. Finally, we show that the gene nifX is not required for nitrogen fixation, in agreement with findings in several bacteria. These studies illustrate the utility of genetic methods in M. maripaludis and show the enhanced perspective that studies in the Archaea can bring to known biological systems.
我们已运用遗传方法对沼泽甲烷球菌中的氮代谢及其调控进行研究。我们提供证据表明，甲烷球菌属和甲烷杆菌属中存在一个“氮调节子”，其中包含氮代谢相关基因，这些基因通过一个共同的阻遏物结合位点序列（即操纵基因）在转录水平上受到协同调控。推测的调控机制类似于细菌中普遍的阻遏模式，但与细菌中通过激活发生的著名氮调控机制形成对比。氮调节子中的基因包括固氮、谷氨酰胺合成酶、（甲基）氨转运、调节蛋白GlnB和氨依赖性NAD合成酶相关基因，以及一个功能未知的基因。我们还研究了两种新型GlnB同源物的功能，它们由固氮产甲烷菌的nif基因簇编码。沼泽甲烷球菌中glnB基因敲除突变产生的表型提供了直接证据，表明类似glnB的基因参与“氨关闭”过程，即在添加氨后对固氮进行转录后抑制。最后，我们表明nifX基因对于固氮并非必需，这与在几种细菌中的研究结果一致。这些研究说明了遗传方法在沼泽甲烷球菌中的实用性，并展示了古菌研究能为已知生物系统带来的新视角。
