Ptashne K, Cohen S N
J Bacteriol. 1975 May;122(2):776-81. doi: 10.1128/jb.122.2.776-781.1975.
Insertion sequence (IS) regions have been identified previously as a cause of strongly polar mutations in Escherichia coli and several bacteriophages. The present experiments indicate that genetically characterized IS regions occur on bacterial plasmid deoxyribonucleic acid (DNA) as both direct and inverted DNA sequence duplications. The DNA insertion which has been shown previously (Sharp et al., 1973) to control expression of tetracycline resistance in the R6-5 plasmid, and which occurs as directly and inversely repeated DNA sequences adjacent to the region believed to contain the tetracycline resistance gene, has been identified as IS3. A second genetically characterized insertion sequence (IS1) has been identified as a direct DNA duplication occurring at both junctions of the resistance transfer factor and R-determinant components of R6-5 and related plasmids. A model is presented for the reversible dissociation of resistance transfer factor and R-determinant components of co-integrate R plasmids at the sites of DNA sequence homology provided by the repeated IS regions.
插入序列（IS）区域先前已被确定为大肠杆菌和几种噬菌体中强极性突变的一个原因。目前的实验表明，经遗传特征鉴定的IS区域以直接和反向DNA序列重复的形式存在于细菌质粒脱氧核糖核酸（DNA）上。先前已证明（夏普等人，1973年）在R6 - 5质粒中控制四环素抗性表达的DNA插入，它以直接和反向重复的DNA序列形式出现，与被认为包含四环素抗性基因的区域相邻，已被鉴定为IS3。第二个经遗传特征鉴定的插入序列（IS1）已被确定为在R6 - 5及相关质粒的抗性转移因子和R - 决定簇组件的两个连接处出现的直接DNA重复。本文提出了一个模型，用于说明共整合R质粒的抗性转移因子和R - 决定簇组件在由重复的IS区域提供的DNA序列同源位点处的可逆解离。
