Stuitje A R, Spelt C E, Veltkamp E, Nijkamp H J
Nature. 1981 Mar 19;290(5803):264-7. doi: 10.1038/290264a0.
The bacteriocinogenic plasmid Clo DF13, originally isolated from Escherichia cloacae, is stably maintained in Escherichia coli to the extent of about 10 copies per cell. Its replication resembles that of many other small, multicopy plasmids; plasmid-encoded protein is not required but plasmid-specific genetic information is involved in regulation of replication as both conditional and nonconditional copy-number mutants of Clo DF13, and transcomplementable copy-number mutants of plasmid Col E1 have been described. The sequences essential for replication of Col E1 (refs 16, 17) and Clo DF13 (refs 18, 19) have been identified within a region surrounding the replication origin. Initiation of Col E1 replication is preceded by transcription of the origin region, providing the RNA primer at the origin. However, transcription in the opposite direction results in a small transcript of approximately 100 nucleotides (RNA-100) for both Col E1 (refs 21, 22) and Clo DF13 (ref. 23). Data suggest that Col E1 RNA-100 acts as a negative control element for the initiation of replication. We show here that single base transitions in the RNA-100 cistron of Clo DF13 can result in a nonconditional increase in plasmid copy-number. Also, sequence analysis has revealed that a specific base transition in a DNA region, apparently involved in both termination and initiation of transcription towards the replication origin, results in a thermosensitive plasmid copy-number.
产细菌素质粒Clo DF13最初从阴沟肠杆菌中分离得到，在大肠杆菌中能稳定维持，每个细胞约有10个拷贝。其复制过程与许多其他小型多拷贝质粒相似；虽然不需要质粒编码的蛋白质，但质粒特异性遗传信息参与复制调控，因为已经报道了Clo DF13的条件性和非条件性拷贝数突变体以及质粒Col E1的可反式互补拷贝数突变体。Col E1（参考文献16、17）和Clo DF13（参考文献18、19）复制所必需的序列已在围绕复制起点的区域内确定。Col E1复制的起始之前是起点区域的转录，在起点处提供RNA引物。然而，相反方向的转录会产生大约100个核苷酸的小转录本（RNA-100），Col E1（参考文献21、22）和Clo DF13（参考文献23）都是如此。数据表明，Col E1 RNA-100作为复制起始的负调控元件。我们在此表明，Clo DF13的RNA-100顺反子中的单碱基转换可导致质粒拷贝数的非条件性增加。此外，序列分析表明，DNA区域中的一个特定碱基转换，显然与朝向复制起点的转录终止和起始都有关，会导致温度敏感型质粒拷贝数。
