Ano T, Imanaka T, Aiba S
Mol Gen Genet. 1986 Mar;202(3):416-20. doi: 10.1007/BF00333271.
The replication control mechanism of Bacillus plasmid pRBH1 was analysed; pRBH1 contains four promoters, P1 to P4, and a large inverted repeat (63 base pairs) upstream of the protein (RepB) coding sequence. The stem and loop structure is surrounded by two promoters, P1 and P3, with different directions of transcription. One base substitution in the loop structure caused a change in copy number. Since the P1 promoter is located upstream of the replication origin of pRBH1, the transcript from the P1 promoter might serve as the primer of DNA replication. In vivo transcription from the P1 promoter was repressed by a trans-acting plasmid gene product. Since the RepB protein is involved in copy number control and RepB contains the consensus amino acid sequence of DNA binding proteins, RepB was thought to be the repressor. It was concluded from these data that the inverted repeat is involved in the control of copy number of the plasmid pRBH1. The RepB protein also contains two regions highly homologous with the Rom protein encoded on Escherichia coli plasmid ColE1. The possible mechanism for the copy number control of the plasmid via RepB protein and/or RNAs is discussed.
对芽孢杆菌质粒pRBH1的复制控制机制进行了分析；pRBH1含有四个启动子，P1至P4，以及蛋白质（RepB）编码序列上游的一个大的反向重复序列（63个碱基对）。茎环结构被两个转录方向不同的启动子P1和P3包围。环结构中的一个碱基替换导致拷贝数发生变化。由于P1启动子位于pRBH1复制起点的上游，P1启动子的转录本可能作为DNA复制的引物。P1启动子在体内的转录受到一种反式作用质粒基因产物的抑制。由于RepB蛋白参与拷贝数控制，且RepB含有DNA结合蛋白的共有氨基酸序列，因此认为RepB是阻遏物。从这些数据可以得出结论，反向重复序列参与了质粒pRBH1拷贝数的控制。RepB蛋白还含有两个与大肠杆菌质粒ColE1上编码的Rom蛋白高度同源的区域。讨论了通过RepB蛋白和/或RNA控制质粒拷贝数的可能机制。
