Aguilar O M, Reiländer H, Arnold W, Pühler A
Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Federal Republic of Germany.
J Bacteriol. 1987 Dec;169(12):5393-400. doi: 10.1128/jb.169.12.5393-5400.1987.
An essential gene for symbiotic nitrogen fixation (fixF) is located near the common nodulation region of Rhizobium meliloti. A DNA fragment carrying fixF was characterized by hybridization with Klebsiella pneumoniae nif DNA and by nucleotide sequence analysis. The fixF gene was found to be related to K. pneumoniae nifN and was therefore renamed as the R. meliloti nifN gene. Upstream of the nifN coding region a second open reading frame was identified coding for a putative polypeptide of 110 amino acids (ORF110). By fragment-specific Tn5 mutagenesis it was shown that the nifN gene and ORF110 form an operon. The control region of this operon contains a nif promoter and also the putative nifA-binding sequence. For the deduced amino acid sequence of the nifN gene product a striking homology to the R. meliloti nifK protein was found. One cysteine residue and its adjacent amino acid sequence, which are highly conserved in the R. meliloti nifK, R. meliloti nifN, and K. pneumoniae nifN proteins, may play a role in binding the FeMo cofactor.
一个参与共生固氮的必需基因（fixF）位于苜蓿根瘤菌的共同结瘤区域附近。通过与肺炎克雷伯氏菌固氮基因DNA杂交以及核苷酸序列分析，对携带fixF的DNA片段进行了表征。发现fixF基因与肺炎克雷伯氏菌的nifN相关，因此将其重新命名为苜蓿根瘤菌的nifN基因。在nifN编码区上游鉴定出第二个开放阅读框，其编码一个由110个氨基酸组成的推定多肽（ORF110）。通过片段特异性Tn5诱变表明，nifN基因和ORF110形成一个操纵子。该操纵子的控制区包含一个固氮启动子以及推定的nifA结合序列。对于nifN基因产物的推导氨基酸序列，发现与苜蓿根瘤菌的nifK蛋白有显著同源性。在苜蓿根瘤菌的nifK、苜蓿根瘤菌的nifN和肺炎克雷伯氏菌的nifN蛋白中高度保守的一个半胱氨酸残基及其相邻氨基酸序列，可能在结合铁钼辅因子中起作用。
