Ditta G, Virts E, Palomares A, Kim C H
J Bacteriol. 1987 Jul;169(7):3217-23. doi: 10.1128/jb.169.7.3217-3223.1987.
Experiments using plasmid-borne gene fusions and direct RNA measurements have revealed that expression from the nifA gene is induced in Rhizobium meliloti when the external oxygen concentration is reduced to microaerobic levels. Induction occurs in the absence of alfalfa and in the presence of fixed nitrogen and does not require ntrC. The production of functional nifA gene product (NifA) can be demonstrated by its ability to activate the nitrogenase promoter P1. Aerobic induction of nifA can also occur during nitrogen starvation at low pH, but in this case induction is dependent on ntrC and does not lead to P1 activation. The data indicate that reduced oxygen tension is potentially a major trigger for symbiotic activation of nitrogen fixation in Rhizobium species.
利用质粒携带的基因融合和直接RNA测量进行的实验表明，当外部氧气浓度降至微需氧水平时，苜蓿根瘤菌中的nifA基因表达会被诱导。诱导在没有苜蓿且存在固定氮的情况下发生，并且不需要ntrC。功能性nifA基因产物（NifA）的产生可以通过其激活固氮酶启动子P1的能力来证明。在低pH值的氮饥饿期间，nifA也可发生需氧诱导，但在这种情况下，诱导依赖于ntrC，且不会导致P1激活。数据表明，降低的氧张力可能是根瘤菌属中固氮共生激活的主要触发因素。
