SEQUENCE AND MOLECULAR ANALYSIS OF THE NIFL GENE OF AZOTOBACTER-VINELANDII
SEQUENCE AND MOLECULAR ANALYSIS OF THE NIFL GENE OF AZOTOBACTER-VINELANDII
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DOI：
10.1111/j.1365-2958.1993.tb01745.x
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发表时间：
1993-08-01
影响因子：
3.6
通讯作者：
KENNEDY, C
中科院分区：
文献类型：
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作者：
BLANCO, G;DRUMMOND, M;KENNEDY, C
在肺炎克雷伯菌和维氏固氮菌中，编码固氮负调节因子的 nifL 基因紧邻 nifA 的上游。我们对 A. vinelandii nifL 基因进行了测序，发现它的 C 末端结构域与组氨酸蛋白激酶 (HPK) 的同源性比肺炎克雷伯菌 NifL 更高。特别是，A. vinelandii NifL 在显示在其他系统中被磷酸化的位置处含有保守的组氨酸。两种 NifL 蛋白的 N 末端均与 Halobacter halobium 蝙蝠基因产物的一部分同源。蝙蝠参与细菌视蛋白的调节，其表达对氧敏感。同一区域与苜蓿根瘤菌 fixL 基因产物（一种氧传感蛋白）的血红素结合 N 端结构域表现出同源性。与肺炎克雷伯菌 NifL 一样，A. vinelandii NifL 可以在 NH4+ 或氧气存在的情况下阻止 nif 基因的表达。因此，在 NifL、FixL 和 Bat 的 C 端区域发现的同源序列可能涉及氧结合或传感。 nifL 编码区的框内缺失突变导致 NH4+ 的抑制作用丧失，并且突变体在固氮过程中分泌大量氨，从而证实了之前报道的插入突变的表型。此外，与肺炎克雷伯菌一样，nifLA 在 A. vinelandii 中共转录，但 A. vinelandii 启动子的表达既不需要 RpoN，也不需要 NtrC。
In both Klebsiella pneumoniae and Azotobacter vinelandii the nifL gene, which encodes a negative regulator of nitrogen fixation, lies immediately upstream of nifA. We have sequenced the A. vinelandii nifL gene and found that it is more homologous in its C-terminal domain to the histidine protein kinases (HPKs) than is K. pneumoniae NifL. In particular A. vinelandii NifL contains a conserved histidine at a position shown to be phosphorylated in other systems. Both NifL proteins are homologous in their N-termini to a part of the Halobacterium halobium bat gene product; Bat is involved in regulation of bacterio-opsin, the expression of which is oxygen sensitive. The same region showed homology to the haem-binding N-terminal domain of the Rhizobium meliloti fixL gene product, an oxygen-sensing protein. Like K. pneumoniae NifL, A. vinelandii NifL is shown here to prevent expression of nif genes in the presence of NH4+ or oxygen. The sequences found homologous in the C-terminal regions of NifL, FixL and Bat might therefore be involved in oxygen binding or sensing. An in-frame deletion mutation in the nifL coding region resulted in loss of repression by NH4+ and the mutant excreted high amounts of ammonia during nitrogen fixation, thus confirming a phenotype reported earlier for an insertion mutation. In addition, nifLA are cotranscribed in A. vinelandii as in K. pneumoniae, but expression from the A. vinelandii promoter requires neither RpoN nor NtrC.