Buikema W J, Klingensmith J A, Gibbons S L, Ausubel F M
J Bacteriol. 1987 Mar;169(3):1120-6. doi: 10.1128/jb.169.3.1120-1126.1987.
Using transposon Tn5-mediated mutagenesis, an essential Rhizobium meliloti nitrogen fixation (nif) gene was identified and located directly downstream of the regulatory gene nifA. Maxicell and DNA sequence analysis demonstrated that the new gene is transcribed in the same direction as nifA and codes for a 54-kilodalton protein. In Klebsiella pneumoniae, the nifBQ operon is located directly downstream of a gene which is structurally and functionally homologous to the R. meliloti nifA gene. The DNA sequences of the K. pneumoniae nifB and nifQ genes (which code for 51- and 20-kilodalton proteins, respectively) were determined. The DNA sequence of the newly identified R. meliloti gene was approximately 50% homologous to the K. pneumoniae nifB gene. R. meliloti does not contain a gene homologous to nifQ directly downstream of nifB. The R. meliloti nifB product shares approximately 40% amino acid homology with the K. pneumoniae nifB product, and 10 of the 12 cysteine residues of the R. meliloti nifB product are conserved with 10 of the 17 cysteine residues of the K. pneumoniae nifB product.
利用转座子Tn5介导的诱变技术，鉴定出了苜蓿根瘤菌一个必需的固氮（nif）基因，该基因直接位于调控基因nifA的下游。大肠杆菌细胞和DNA序列分析表明，这个新基因与nifA同向转录，编码一个54千道尔顿的蛋白质。在肺炎克雷伯菌中，nifBQ操纵子直接位于一个与苜蓿根瘤菌nifA基因在结构和功能上同源的基因下游。测定了肺炎克雷伯菌nifB和nifQ基因的DNA序列（分别编码51千道尔顿和20千道尔顿的蛋白质）。新鉴定出的苜蓿根瘤菌基因的DNA序列与肺炎克雷伯菌nifB基因约有50%的同源性。苜蓿根瘤菌在nifB的直接下游不含与nifQ同源的基因。苜蓿根瘤菌nifB产物与肺炎克雷伯菌nifB产物有大约40%的氨基酸同源性，苜蓿根瘤菌nifB产物的12个半胱氨酸残基中有10个与肺炎克雷伯菌nifB产物的17个半胱氨酸残基中的10个保守。
