Iismaa S E, Ealing P M, Scott K F, Watson J M
CSIRO Division of Plant Industry, Canberra City, ACT, Australia.
Mol Microbiol. 1989 Dec;3(12):1753-64. doi: 10.1111/j.1365-2958.1989.tb00161.x.
Nucleotide sequence analysis of a 2.5kb region downstream of the nifA gene from Rhizobium leguminosarum biovar trifolii has resulted in linkage, at the DNA sequence level, of the nifEN, nifHDK, fixABCX, nifA gene cluster with the nodEF, nodD, nodABCIJ genes. Four genes have been identified within this intervening region. Immediately 3' to the nifA gene is the nifB gene and the nifB-linked ferredoxin-encoding fdxN gene. Downstream of fdxN in R. leguminosarum bv. trifolii and in Rhizobium meliloti, we have identified an open reading frame which has not been described previously and which we propose to designate fixU. Downstream of fixU in R. leguminosarum bv. trifolii is a nod gene, nodT, which is contiguous with nodJ (B. Surin et al., manuscript in preparation). As a result of this study, the linkage relationships of 22 symbiotic genes spanning a 24 kb region of the symbiotic plasmid from R. leguminosarum bv. trifolii are now known.
对来自三叶草根瘤菌生物变种三叶草的nifA基因下游2.5kb区域进行核苷酸序列分析，结果表明，在DNA序列水平上，nifEN、nifHDK、fixABCX、nifA基因簇与nodEF、nodD、nodABCIJ基因存在连锁关系。在这个间隔区域内已鉴定出四个基因。紧接在nifA基因3'端的是nifB基因以及与nifB连锁的编码铁氧还蛋白的fdxN基因。在三叶草根瘤菌生物变种三叶草和苜蓿根瘤菌中，fdxN基因下游，我们鉴定出一个此前未描述过的开放阅读框，我们提议将其命名为fixU。在三叶草根瘤菌生物变种三叶草中，fixU基因下游是一个nod基因nodT，它与nodJ相邻（B. 苏林等人，正在准备的手稿）。这项研究的结果使我们现在了解了来自三叶草根瘤菌生物变种三叶草共生质粒24kb区域内22个共生基因的连锁关系。
