School of Biological Sciences, Seoul National University, Seoul, 151-747, Korea.
Arch Microbiol. 2012 Jan;194(1):29-34. doi: 10.1007/s00203-011-0732-7. Epub 2011 Jul 17.
The nucleotide sequence of a 20.5-kb genomic region harboring nif genes was determined and analyzed. The fragment was obtained from Frankia sp. EuIK1 strain, an indigenous symbiont of Elaeagnus umbellata. A total of 20 ORFs including 12 nif genes were identified and subjected to comparative analysis with the genome sequences of 3 Frankia strains representing diverse host plant specificities. The nucleotide and deduced amino acid sequences showed highest levels of identity with orthologous genes from an Elaeagnus-infecting strain. The gene organization patterns around the nif gene clusters were well conserved among all 4 Frankia strains. However, characteristic features appeared in the location of the nifV gene for each Frankia strain, depending on the type of host plant. Sequence analysis was performed to determine the transcription units and suggested that there could be an independent operon starting from the nifW gene in the EuIK strain. Considering the organization patterns and their total extensions on the genome, we propose that the nif gene clusters remained stable despite genetic variations occurring in the Frankia genomes.
该片段来自于 Elaeagnus umbellata 的本土共生菌 Frankia sp. EuIK1 菌株，我们对其 20.5kb 基因组区域的核苷酸序列进行了测定和分析。共鉴定出 20 个 ORF，包括 12 个 nif 基因，并与代表不同宿主植物特异性的 3 株 Frankia 菌株的基因组序列进行了比较分析。核苷酸和推导的氨基酸序列与从一株感染 Elaeagnus 的菌株中获得的同源基因具有最高的同一性。nif 基因簇周围的基因组织模式在所有 4 株 Frankia 菌株中都得到了很好的保守。然而，nifV 基因在每个 Frankia 菌株中的位置出现了特征性的差异，这取决于宿主植物的类型。序列分析确定了转录单位，并表明在 EuIK 菌株中，nifW 基因可能存在一个独立的操纵子。考虑到它们在基因组上的组织模式和总长度，我们提出尽管 Frankia 基因组中发生了遗传变异，但 nif 基因簇仍然保持稳定。
