Hartl D L, Sawyer S A
Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63110.
Genetics. 1988 Mar;118(3):537-41. doi: 10.1093/genetics/118.3.537.
Natural isolates of Escherichia coli are polymorphic for the presence or absence of insertion sequences. Among the ECOR reference collection of 71 natural isolates studied for the number of copies of the insertion sequences IS1, IS2, IS3, IS4, IS5 and IS30, the number of strains containing no copies of the insertion sequences were 11, 28, 23, 43, 46 and 36, respectively. Significant correlations occur in the ECOR strains in the presence or absence of unrelated insertion sequences in the chromosome and plasmid complements. Strains containing any insertion sequence are more likely to contain additional, unrelated insertion sequences than would be expected by chance. We suggest that the positive correlations result from horizontal transfer mediated by plasmids. A branching-process model for the plasmid-mediated transmission of insertion sequences among hosts yields such a correlation, even in the absence of interactions affecting transposition or fitness. The predictions of the model are quantitatively in agreement with the observed correlations among insertion sequences.
大肠杆菌的自然分离株对于插入序列的存在与否具有多态性。在对71株自然分离株组成的ECOR参考菌株集合进行研究，以确定插入序列IS1、IS2、IS3、IS4、IS5和IS30的拷贝数时，不含插入序列拷贝的菌株数分别为11、28、23、43、46和36。在ECOR菌株中，染色体和质粒互补物中无关插入序列的存在与否存在显著相关性。含有任何插入序列的菌株比随机预期更有可能含有额外的、无关的插入序列。我们认为这种正相关是由质粒介导的水平转移导致的。一个用于质粒介导的插入序列在宿主间传播的分支过程模型产生了这样的相关性，即使在没有影响转座或适应性的相互作用的情况下也是如此。该模型的预测在数量上与观察到的插入序列之间的相关性一致。
