Bali A, Blanco G, Hill S, Kennedy C
Nitrogen Fixation Laboratory, University of Sussex, Brighton, United Kingdom.
Appl Environ Microbiol. 1992 May;58(5):1711-8. doi: 10.1128/aem.58.5.1711-1718.1992.
A mutation in the gene upstream of nifA in Azotobacter vinelandii was introduced into the chromosome to replace the corresponding wild-type region. The resulting mutant, MV376, produced nitrogenase constitutively in the presence of 15 mM ammonium. When introduced into a nifH-lacZ fusion strain, the mutation permitted beta-galactosidase production in the presence of ammonium. The gene upstream of nifA is therefore designated nifL because of its similarity to the Klebsiella pneumoniae nifL gene in proximity to nifA, in mutant phenotype, and in amino acid sequence of the gene product. The A. vinelandii nifL mutant MV376 excreted significant quantities of ammonium (approximately 10 mM) during diazotrophic growth. In contrast, ammonium excretion during diazotrophy was much lower in a K. pneumoniae nifL deletion mutant (maximum, 0.15 mM) but significantly higher than in NifL+ K. pneumoniae. The expression of the A. vinelandii nifA gene, unlike that of K. pneumoniae, was not repressed by ammonium.
将维涅兰德固氮菌中nifA上游基因的一个突变引入染色体，以取代相应的野生型区域。所得突变体MV376在15 mM铵存在的情况下组成型产生固氮酶。当将该突变引入nifH - lacZ融合菌株时，该突变允许在铵存在的情况下产生β-半乳糖苷酶。因此，nifA上游的基因被命名为nifL，因为它在与nifA的邻近性、突变表型以及基因产物的氨基酸序列方面与肺炎克雷伯氏菌的nifL基因相似。维涅兰德固氮菌的nifL突变体MV376在固氮生长期间分泌大量的铵（约10 mM）。相比之下，肺炎克雷伯氏菌的nifL缺失突变体在固氮期间的铵排泄量要低得多（最高0.15 mM），但明显高于NifL +的肺炎克雷伯氏菌。与肺炎克雷伯氏菌不同，维涅兰德固氮菌nifA基因的表达不受铵的抑制。
