Kaminski P A, Mandon K, Arigoni F, Desnoues N, Elmerich C
Unité de Physiologie Cellulaire, Institut Pasteur, Paris, France.
Mol Microbiol. 1991 Aug;5(8):1983-91. doi: 10.1111/j.1365-2958.1991.tb00820.x.
The nucleotide sequence of a 1 kb fragment upstream of Azorhizobium caulinodans fixL was established. An open reading frame of 744 bp was identified as a fixK homologue. A kanamycin cartridge was inserted into the cloned fixK-like gene and recombined into the host genome. The resulting mutant was Nif-Fix-, suggesting that FixK was required for nitrogen fixation both in symbiotic conditions and in the free-living state. Using a pfixK-lacZ fusion, the FixLJ products were shown to control the expression of fixK. Using a pnifA-lacZ fusion, the FixK product was shown to regulate positively the transcription of nifA in bacteria grown in the free-living state. In addition, a double ntrC-fixL mutant was constructed and was shown to be completely devoid of nitrogenase activity. A model of regulation, based on these data, is presented and might explain the unusual ability of A. caulinodans to fix nitrogen both under symbiotic conditions and in the free-living state.
确定了茎瘤固氮根瘤菌fixL上游1 kb片段的核苷酸序列。一个744 bp的开放阅读框被鉴定为fixK同源物。将卡那霉素盒插入克隆的类fixK基因中，并重组到宿主基因组中。所得突变体为固氮-固着-型，表明FixK在共生条件和自由生活状态下的固氮过程中都是必需的。使用pfixK-lacZ融合体，显示FixLJ产物可控制fixK的表达。使用pnifA-lacZ融合体，显示FixK产物在自由生活状态下生长的细菌中可正向调节nifA的转录。此外，构建了双ntrC-fixL突变体，结果显示其完全没有固氮酶活性。基于这些数据，提出了一个调控模型，该模型可能解释了茎瘤固氮根瘤菌在共生条件和自由生活状态下固氮的特殊能力。
