Multiple chromosomes in bacteria. The yin and yang of trp gene localization in Rhodobacter sphaeroides 2.4.1.
Multiple chromosomes in bacteria. The yin and yang of trp gene localization in Rhodobacter sphaeroides 2.4.1.
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细菌中有多个染色体。
DOI：
10.1093/genetics/153.2.525
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发表时间：
1999
期刊：
影响因子：
3.3
通讯作者：
Kaplan,S
中科院分区：
文献类型：
--
作者：
Mackenzie,C;Simmons,AE;Kaplan,S
细菌中存在多条染色体已经有一段时间了。然而，不同染色体之间的功能团结程度仍然未知。为了研究这个问题，我们调查了多染色体光合真杆菌Rhodobacter sphaeroides 2.4.1中色氨酸生物合成途径的已充分描述的基因。使用Tn 5对该生物体的基因组进行诱变，并分离出色氨酸（Trp-）营养缺陷型菌株。脉冲场凝胶作图表明，Tn 5插入在大（3 Mb CI）和小（0.9 Mb CII）染色体创建一个色氨酸表型。对Tn 5插入位点两侧的DNA进行测序表明，基因trpE-yibQ-trpGDC位于CI上的基因座，而基因trpF-aroR-trpB位于CII上的基因座。出乎意料的是，在trpB下游没有发现trpA。相反，将其置于CI物理图谱上距离trpE-yibQ-trpGDC 1.23 Mb的基因座处。将R.为了将类球孢菌trp基因与其它细菌的trp基因进行比较，对两条染色体上trp基因周围的DNA区域进行了测序。特别重要的是发现rpsA 1，它编码核糖体蛋白S1，和cmkA，它编码胞苷酸单磷酸激酶，在CII。这些基因被认为分别对翻译和染色体复制至关重要。Southern杂交结果表明，trp基因和rpsA 1基因在基因组中以单拷贝存在。到目前为止，色氨酸操纵子的拓扑结构在细菌基因组中是独一无二的。当采取的发现，CII编码基本的管家功能，总的印象是这些染色体之间的密切监管和功能整合之一。
The existence of multiple chromosomes in bacteria has been known for some time. Yet the extent of functional solidarity between different chromosomes remains unknown. To examine this question, we have surveyed the well-described genes of the tryptophan biosynthetic pathway in the multichromosomal photosynthetic eubacterium Rhodobacter sphaeroides 2.4.1. The genome of this organism was mutagenized using Tn5, and strains that were auxotrophic for tryptophan (Trp-) were isolated. Pulsed-field gel mapping indicated that Tn5 insertions in both the large (3 Mb CI) and the small (0.9 Mb CII) chromosomes created a Trp-phenotype. Sequencing the DNA flanking the sites of the Tn5 insertions indicated that the genes trpE-yibQ-trpGDC were at a locus on CI, while genes trpF-aroR-trpB were at locus on CII. Unexpectedly, trpA was not found downstream of trpB. Instead, it was placed on the CI physical map at a locus 1.23 Mb away from trpE-yibQ-trpGDC. To relate the context of the R. sphaeroides trp genes to those of other bacteria, the DNA regions surrounding the trp genes on both chromosomes were sequenced. Of particular significance was the finding that rpsA1, which encodes ribosomal protein S1, and cmkA, which encodes cytidylate monophosphate kinase, were on CII. These genes are considered essential for translation and chromosome replication, respectively. Southern blotting suggested that the trp genes and rpsA1 exist in single copy within the genome. To date, this topological organization of the trp “operon” is unique within a bacterial genome. When taken with the finding that CII encodes essential housekeeping functions, the overall impression is one of close regulatory and functional integration between these chromosomes.