Scolnik P A, Haselkorn R
Nature. 1984;307(5948):289-92. doi: 10.1038/307289a0.
Biological nitrogen fixation requires the nitrogenase enzyme complex, ATP, and a strong reductant. Klebsiella pneumoniae contains 15 linked nitrogen fixation (nif) genes, three of which, nifH, nifD and nifK have been sufficiently conserved in evolution that cloned K. pneumoniae nifHDK DNA will hybridize to DNA sequences from every nitrogen-fixing bacterium examined to date, including the purple, non-sulphur bacterium Rhodopseudomonas capsulata, in which one complete nifHDK operon has been mapped. Using cloned K. pneumoniae nifHDK DNA we report here that R. capsulata contains multiple copies of the genes for nitrogenase components. Two regions containing sequences homologous to all three nif structural genes have been identified, and mutations in one region produced a Nif- phenotype. Nif+ pseudorevertants were derived from these mutants, some of which retained the original mutation suggesting that some of the extra nif gene sequences can be functionally activated.
生物固氮需要固氮酶复合物、ATP和强还原剂。肺炎克雷伯菌含有15个连锁的固氮（nif）基因，其中3个基因，即nifH、nifD和nifK在进化过程中得到了充分的保守，以至于克隆的肺炎克雷伯菌nifHDK DNA能与迄今为止检测的每一种固氮细菌的DNA序列杂交，包括紫色非硫细菌荚膜红假单胞菌，在该菌中已定位了一个完整的nifHDK操纵子。利用克隆的肺炎克雷伯菌nifHDK DNA，我们在此报告荚膜红假单胞菌含有固氮酶组分基因的多个拷贝。已鉴定出两个含有与所有三个nif结构基因同源序列的区域，其中一个区域的突变产生了固氮缺陷型（Nif-）表型。Nif+假回复体来源于这些突变体，其中一些保留了原始突变，这表明一些额外的nif基因序列可以被功能性激活。
