Stueber D, Bujard H
EMBO J. 1982;1(11):1399-404. doi: 10.1002/j.1460-2075.1982.tb01329.x.
The copy number of plasmids containing the ColE1 replicon is affected by changes in the transcriptional activity within the plasmid if these changes lead to transcriptional readthrough into the replication region towards the promoter priming DNA replication. Such readthrough e.g., from the tet region in pBR322 not only causes overproduction of a peptide known to affect the copy number negatively but also appears to interfere negatively with the replication of the plasmid itself. The proper placement of efficient transcriptional terminators prevents such interference and permits the stable integration of strong promoters. Due to this termination effect, up to 9-fold differences in plasmid copy number were observed, depending upon the particular growth conditions. The higher copy number is of course reflected by higher yields of plasmid-specified gene products indicating the relevance of the above effects for studies of gene expression.
含有ColE1复制子的质粒拷贝数会受到质粒内转录活性变化的影响，前提是这些变化导致转录通读进入朝向启动子引发DNA复制的复制区域。例如，来自pBR322中tet区域的这种通读不仅会导致已知对拷贝数有负面影响的肽过量产生，而且似乎还会对质粒本身的复制产生负面影响。高效转录终止子的正确放置可防止这种干扰，并允许强启动子的稳定整合。由于这种终止效应，根据特定的生长条件，观察到质粒拷贝数存在高达9倍的差异。当然，较高的拷贝数会反映在质粒指定基因产物的较高产量上，这表明上述效应与基因表达研究的相关性。
