Wang S Z, Dean D R, Chen J S, Johnson J L
Department of Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg 24061.
J Bacteriol. 1991 May;173(10):3041-6. doi: 10.1128/jb.173.10.3041-3046.1991.
The nifV gene products from Azotobacter vinelandii and Klebsiella pneumoniae share a high level of primary sequence identity and are proposed to catalyze the synthesis of homocitrate. While searching for potential nif (nitrogen fixation) genes within the genomic region located downstream from the nifN-B gene of Clostridium pasteurianum, we observed two open reading frames (ORFs) whose deduced amino acid sequences exhibit nonoverlapping sequence identity to different portions of the nifV gene products from A. vinelandii and K. pneumoniae. Conserved regions were located between the C-terminal 195 amino acid residues of the first ORF and the C-terminal portion of the nifV gene product and between the entire sequence of the second ORF (269 amino acid residues) and the N-terminal portion of the nifV gene product. We therefore designated the first ORF nifV omega and the second ORF nifV alpha. The deduced amino acid sequences of nifV omega and nifV alpha were also found to have sequence similarity when compared with the primary sequence of the leuA gene product from Salmonella typhimurium, which encodes alpha-isopropylmalate synthase. Marker rescue experiments were performed by recombining nifV omega and nifV alpha from C. pasteurianum, singly and in combination, into the genome of an A. vinelandii mutant strain which has an insertion and a deletion mutation located within its nifV gene. A NifV+ phenotype was obtained only when both the C. pasteurianum nifV omega and nifV alpha genes were introduced into the chromosome of this mutant strain. These results suggest that the nifV omega and nifV alpha genes encode separate domains, both of which are required for homocitrate synthesis in C. pasteurianum.
来自棕色固氮菌和肺炎克雷伯菌的nifV基因产物具有高度的一级序列同一性，并被认为催化高柠檬酸的合成。在巴斯德梭菌nifN - B基因下游的基因组区域中寻找潜在的nif（固氮）基因时，我们观察到两个开放阅读框（ORF），其推导的氨基酸序列与来自棕色固氮菌和肺炎克雷伯菌的nifV基因产物的不同部分表现出不重叠的序列同一性。保守区域位于第一个ORF的C端195个氨基酸残基与nifV基因产物的C端部分之间，以及第二个ORF的整个序列（269个氨基酸残基）与nifV基因产物的N端部分之间。因此，我们将第一个ORF命名为nifVω，第二个ORF命名为nifVα。与编码α - 异丙基苹果酸合酶的鼠伤寒沙门氏菌leuA基因产物的一级序列相比，nifVω和nifVα推导的氨基酸序列也具有序列相似性。通过将来自巴斯德梭菌的nifVω和nifVα单独或组合重组到棕色固氮菌突变株的基因组中进行标记拯救实验，该突变株在其nifV基因内有一个插入和一个缺失突变。只有当将巴斯德梭菌的nifVω和nifVα基因都导入该突变株的染色体时，才获得了NifV +表型。这些结果表明，nifVω和nifVα基因编码不同的结构域，这两个结构域都是巴斯德梭菌中高柠檬酸合成所必需的。
