Haack K R, Roth J R
Department of Biology, University of Utah, Salt Lake City 84112, USA.
Genetics. 1995 Dec;141(4):1245-52. doi: 10.1093/genetics/141.4.1245.
Spontaneous tandem chromosomal duplications are common in populations of Escherichia coli and Salmonella typhimurium. They range in frequency for a given locus from 10(-2) to 10(-4) and probably form by RecA-dependent unequal sister strand exchanges between repetitive sequences in direct order. Certain duplications have been observed previously to confer a growth advantage under specific selective conditions. Tandem chromosomal duplications are unstable and are lost at high frequencies, representing a readily reversible source of genomic variation. Six copies of a small mobile genetic element IS200 are evenly distributed around the chromosome of S. typhimurium strain LT2. A survey of 120 independent chromosomal duplications (20 for each of six loci) revealed that recombination between IS200 elements accounted for the majority of the duplications isolated for three of the loci tested. Duplications of the his operon were almost exclusively due to recombination between repeated IS200 elements. These data add further support to the idea that mobile genetic elements provide sequence repeats that play an important role in recombinational chromosome rearrangements, which may contribute to adaptation of bacteria to stressful conditions.
自发串联染色体重复在大肠杆菌和鼠伤寒沙门氏菌群体中很常见。对于给定基因座，其频率范围为10^(-2)至10^(-4)，可能是由RecA依赖的同向重复序列之间的不等姐妹链交换形成的。先前已观察到某些重复在特定选择条件下赋予生长优势。串联染色体重复是不稳定的，会以高频率丢失，是基因组变异的一个易于逆转的来源。小移动遗传元件IS200的六个拷贝均匀分布在鼠伤寒沙门氏菌LT2菌株的染色体周围。对120个独立染色体重复（六个基因座各20个）的调查显示，IS200元件之间的重组占所测试的三个基因座分离出的重复的大部分。组氨酸操纵子的重复几乎完全是由于重复的IS200元件之间的重组。这些数据进一步支持了移动遗传元件提供序列重复的观点，这些重复在重组染色体重排中起重要作用，这可能有助于细菌适应压力条件。
