Ogawa T, Okazaki T
Department of Molecular Biology, School of Science, Nagoya University, Japan.
Mol Gen Genet. 1991 Nov;230(1-2):193-200. doi: 10.1007/BF00290668.
The origin of replication of the Escherichia coli chromosome (oriC) is located in an intercistronic region between the gidA and the mioC genes. The possibility that transcription from the promoters of these two genes is involved in minichromosome replication was examined. Inactivation of the gid promoter led to a reduction in transformation frequency with an oriC plasmid but inactivation of the mioC promoter did not. The decrease in transformation frequency was most pronounced when both promoters were inactive. Under conditions that selected for plasmid-harboring cells, mutation of the gid promoter caused efficient multimerization or integration of oriC plasmids into the chromosomal oriC region and loss of free plasmid molecules. These changes in plasmid structure were also observed, albeit less frequently, with some plasmids defective in mioC promoter activity. In an in vitro DNA replication system for oriC DNA, plasmids with a defective gid promoter had greatly reduced template activity and essentially no replication occurred when both promoters were inactive. These results suggest that coupled transcription starting from the gid as well as the mioC promoter activates initiation of plasmid replication, the major contribution being made by gid transcription. These two promoters are suggested to be under stringent control.
大肠杆菌染色体的复制起点（oriC）位于gidA基因和mioC基因之间的基因间区域。研究了这两个基因启动子的转录是否参与微型染色体复制。gid启动子失活导致携带oriC质粒的转化频率降低，但mioC启动子失活则不会。当两个启动子均无活性时，转化频率的降低最为明显。在选择携带质粒细胞的条件下，gid启动子的突变导致oriC质粒高效多聚化或整合到染色体oriC区域，并导致游离质粒分子丢失。在一些mioC启动子活性有缺陷的质粒中也观察到了质粒结构的这些变化，尽管频率较低。在oriC DNA的体外DNA复制系统中，gid启动子有缺陷的质粒模板活性大大降低，当两个启动子均无活性时基本上不发生复制。这些结果表明，从gid和mioC启动子开始的偶联转录激活了质粒复制的起始，主要贡献来自gid转录。这两个启动子被认为受到严格控制。
