Riess G, Masepohl B, Puehler A
Plasmid. 1983 Sep;10(2):111-8. doi: 10.1016/0147-619x(83)90063-x.
Escherichia coli plasmids like pACYC184 or pBR325 can be mobilized by the P-type plasmid R68.45, which carries a tandem duplication of insertion element IS21, at a frequency of 10(-3)-10(-5) per donor cell. Analysis of exconjugant cells revealed that plasmid mobilization occurs via cointegrate formation involving transposition of IS21. No resolution of cointegrates of pACYC184 and the P-type plasmid could be found in recA recipient cells. In the cointegrate, the E. coli plasmid is flanked by single copies of IS21 in direct orientation. After resolution of the cointegrate in recA+ recipients, the mobilizing plasmid R68.45 lost one copy of IS21 becoming indistinguishable from plasmid R68. It was shown that during mobilization, insertion element IS21 transposes to the mobilized plasmid. Insertion sites and orientations of IS21 in 33 pACYC184::IS21 insertion mutants have been determined: IS21 was found to be integrated in plasmid pACYC184 in different regions but only in one orientation. The IS21 tandem structure of plasmid R68.45 and its role in the mobilization process is discussed.
像pACYC184或pBR325这样的大肠杆菌质粒可被携带插入元件IS21串联重复序列的P型质粒R68.45以每个供体细胞10^(-3)-10^(-5)的频率进行转移。对接合后细胞的分析表明，质粒转移是通过涉及IS21转座的共整合体形成来实现的。在recA受体细胞中未发现pACYC184与P型质粒共整合体的解离现象。在共整合体中，大肠杆菌质粒两侧是直接排列的单拷贝IS21。在recA+受体中解离共整合体后，转移性质粒R68.45失去了一个IS21拷贝，变得与质粒R68无法区分。结果表明，在转移过程中，插入元件IS21转座到了被转移的质粒上。已确定了33个pACYC184::IS21插入突变体中IS21的插入位点和方向：发现IS21整合在质粒pACYC184的不同区域，但只有一种方向。本文讨论了质粒R68.45的IS21串联结构及其在转移过程中的作用。
