Highly plastic chromosomal organization in Salmonella typhi
Highly plastic chromosomal organization in Salmonella typhi
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DOI：
10.1073/pnas.93.19.10303
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发表时间：
1996-09-17
影响因子：
11.1
通讯作者：
Sanderson, KE
中科院分区：
文献类型：
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作者：
Liu, SL;Sanderson, KE
大肠杆菌K-12和鼠伤寒沙门氏菌LT2以及许多其他沙门氏菌的染色体上的基因序列是高度保守的，尽管它们的属在大约1.6亿年前就发生了分化，但伤寒沙门氏菌的染色体DNA被部分消化，用I-CeuI内切酶和脉冲场凝胶电泳法分离DNA片段，结果表明，由于编码核糖体RNA的7个rrn基因之间的同源重组，独立的伤寒杆菌野生型分离株的染色体发生了重排。I-CeuI片段内的基因序列基本保守，但染色体上的片段序列发生了重排，在127株野生型菌株中检测到21个不同顺序的I-CeuI片段，没有发现重复和缺失，但转位和倒位很常见。在野生型菌株中，经常检测到I-CeuI片段转座到距离复制起点(ORIC)不变的位置，但将I-CeuI片段移位到距离ORIC更远的位置的转座非常罕见，这支持了基因剂量假说，即距离ORIC不同的基因具有不同的基因剂量，因此不同的基因表达进化基因适应于其特定的位置；因此，由于转位而改变基因位置的细胞可能不太适合，因此，基因剂量可能是维持基因秩序的力量之一，尽管它在伤寒沙门氏菌中的影响似乎没有其他肠道细菌那么强烈，但基因剂量和基因组平衡假说都需要进一步研究，后者指出复制的起点(ORIC)和终点(TER)必须分开180摄氏度。
Gene order in the chromosomes of Escherichia coli K-12 and Salmonella typhimurium LT2, and in many other species of Salmonella, is strongly conserved, even though the genera diverged about 160 million years ago, However, partial digestion of chromosomal DNA of Salmonella typhi, the causal organism of typhoid fever, with the endonuclease I-CeuI followed by separation of the DNA fragments by pulsed-field gel electrophoresis showed that the chromosomes of independent wild-type isolates of S. typhi are rearranged due to homologous recombination between the seven rrn genes that code for ribosomal RNA. The order of genes within the I-CeuI fragments is largely conserved, but the order of the fragments on the chromosome is rearranged, Twenty-one different orders of the I-CeuI fragments were detected among the 127 wild-type strains we examined, Duplications and deletions were not found, but transpositions and inversions were common. Transpositions of I-CeuI fragments into sites that do not change their distance from the origin of replication (oriC) are frequently detected among the wild-type strains, but transpositions that move the fragments much further from oriC mere rare, This supports the gene dosage hypothesis that genes at different distances from oriC have different gene dosages and, hence, different gene expression evolution genes become adapted to their specific location; thus, cells with changes in gene location due to transpositions may be less fit, Therefore, gene dosage may be one of the forces that conserves gene order, although its effects seem less strong in S. typhi than in other enteric bacteria, However, both the gene dosage and the genomic balance hypotheses, the latter of which states that the origin (oriC) and terminus (TER) of replication must be separated by 180 degrees C, need further investigation.