Thomas C M, Cross M A, Hussain A A, Smith C A
EMBO J. 1984 Jan;3(1):57-63. doi: 10.1002/j.1460-2075.1984.tb01761.x.
Broad host-range plasmid RK2 is able to replicate in a controlled manner in most Gram negative bacterial species. To analyze the elements of its control mechanism, we have measured the copy number in Escherichia coli of mini-RK2 replicons isogenic except for defined deletions in regions adjacent to the vegetative replication origin, oriVRK2, which have previously been implicated in copy number control because of their expression of plasmid incompatibility. The results indicate that while the previously defined 700-bp HaeII oriVRK2 fragment carries one copy control element (copA), a second (copB) lies at least partly outside this fragment towards the tetracycline resistance genes of RK2. Deletions affecting both these regions give a mini replicon with a copy number of 35-40 compared with 4-7 for parental RK2. Further incompatibility experiments indicate that targets for both incA (copA) and incB (copB) lie within the 700-bp HaeII oriVRK2 fragment.
广宿主范围质粒RK2能够在大多数革兰氏阴性细菌物种中以可控方式复制。为了分析其控制机制的元件，我们测定了除了与营养复制起点oriVRK2相邻区域存在特定缺失外其余均同基因的mini-RK2复制子在大肠杆菌中的拷贝数，由于这些区域表达质粒不相容性，此前已认为它们与拷贝数控制有关。结果表明，虽然先前定义的700-bp HaeII oriVRK2片段携带一个拷贝控制元件（copA），但第二个（copB）至少部分位于该片段之外，朝向RK2的四环素抗性基因。影响这两个区域的缺失产生了一个mini复制子，其拷贝数为35 - 40，而亲本RK2的拷贝数为4 - 7。进一步的不相容性实验表明，incA（copA）和incB（copB）的靶点都在700-bp HaeII oriVRK2片段内。
