BRADYRHIZOBIUM-JAPONICUM HAS 2 DIFFERENTIALLY REGULATED, FUNCTIONAL HOMOLOGS OF THE SIGMA-54 GENE (RPON)
BRADYRHIZOBIUM-JAPONICUM HAS 2 DIFFERENTIALLY REGULATED, FUNCTIONAL HOMOLOGS OF THE SIGMA-54 GENE (RPON)
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DOI：
10.1128/jb.173.3.1125-1138.1991
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发表时间：
1991-02-01
影响因子：
3.2
通讯作者：
FISCHER, HM
中科院分区：
文献类型：
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作者：
KULLIK, I;FRITSCHE, S;FISCHER, HM
RNA聚合酶识别-24/-12型启动子需要一种特殊的sigma因子，sigma-54(RpoN NTRA GLNF)。在固氮大豆共生菌慢生根瘤菌中，鉴定和测序了两个高度保守的rpoN基因(rpoN1和rpoN2)。这两个预测的日本血吸虫RpoN蛋白序列有87%的同源性，并且都显示出与其他细菌的RpoN蛋白不同程度的同源性。在rpoN1下游(但不在rpoN1下游)，发现了另外两个开放阅读框，它们对应于肺炎克雷伯菌和恶臭假单胞菌中位于相似位置的开放阅读框。这两个日本根瘤菌rpoN基因都补充了紫花苜蓿根瘤菌rpoN突变体的琥珀酸和硝酸盐阴性表型。携带单个或双个rpoN突变的菌株仍然能够利用C4-二羧酸盐作为碳源，利用组氨酸、脯氨酸或精氨酸作为氮源，而同化硝酸盐的能力需要表达两个rpoN基因中的至少一个。在共生中，两个rpoN基因可以在功能上相互替代。RpoN1/2双突变体在大豆上诱导的根瘤数量约为野生型的两倍，这些根瘤完全缺乏固氮活性。在rpoN1/2突变体背景中，nifH‘-LacZ融合的转录没有激活，而该突变体中FixR’-LacZ融合的表达仅受到轻微影响。通过rpoN‘-LacZ融合，rpon1的表达在微需氧环境中被激活，至少是有氧环境中的7倍，并且这种类型的调节涉及FixLJ。在所有测试条件下都观察到了rpoN2的表达，并且在rpoN2突变体中表达增加了五倍。这些数据表明，rpoN1基因是受氧调节的，而rpoN2基因是负自我调节的。
Recognition of -24/-12-type promoters by RNA polymerase requires a special sigma factor, sigma-54 (RpoN NtrA GlnF). In the nitrogen-fixing soybean symbiont Bradyrhizobium japonicum, two functional, highly conserved rpoN genes (rpoN1 and rpoN2) were identified and sequenced. The two predicted B. japonicum RpoN protein sequences were 87% identical, and both showed different levels of homology to the RpoN proteins of other bacteria. Downstream of rpoN2 (but not of rpoN1), two additional open reading frames were identified that corresponded to open reading frames located at similar positions in Klebsiella pneumoniae and Pseudomonas putida. Both B. japonicum rpoN genes complemented the succinate- and nitrate-negative phenotypes of a Rhizobium meliloti rpoN mutant. B. japonicum strains carrying single or double rpoN mutations were still able to utilize C4-dicarboxylates as a carbon source and histidine, proline, or arginine as a nitrogen source, whereas the ability to assimilate nitrate required expression of at least one of the two rpoN genes. In symbiosis both rpoN genes could replace each other functionally. The rpoN1/2 double mutant induced about twice as many nodules on soybeans as did the wild type, and these nodules lacked nitrogen fixation activity completely. Transcription of a nifH'-'lacZ fusion was not activated in the rpoN1/2 mutant background, whereas expression of a fixR'-lacZ fusion in this mutant was affected only marginally. By using rpoN'-lacZ fusions, rpon1 expression was shown to be activated at least sevenfold in microaerobiosis as compared with that in aerobiosis, and this type of regulation involved fixLJ. Expression of rpoN2 was observed under all conditions tested and was increased fivefold in an rpoN2 mutant. The data suggested that the rpoN1 gene was regulated in response to oxygen, whereas the rpoN2 gene was negatively autoregulated.