del Solar G H, de al Campa A G, Pérez-Martín J, Choli T, Espinosa M
Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
Nucleic Acids Res. 1989 Apr 11;17(7):2405-20. doi: 10.1093/nar/17.7.2405.
The promiscuous streptococcal plasmid pLS1 encodes for the 5.1 kDa RepA protein, involved in the regulation of the plasmid copy number. Synthesis of RepA was observed both in Bacillus subtilis minicells and in an Escherichia coli expression system. From this system, the protein has been purified and it appears to be a dimer of identical subunits. The amino acid sequence of RepA has been determined. RepA shows the alpha helix-turn-alpha helix motif typical of many DNA-binding proteins and it shares homology with a number of repressors, specially with the TrfB repressor encoded by the broad-host-range plasmid RK2. DNase I footprinting revealed that the RepA target is located in the region of the promoter for the repA and repB genes. Trans-complementation analysis showed that in vivo, RepA behaves as a repressor by regulating the plasmid copy number. We propose that the regulatory role of RepA is by limitation of the synthesis of the initiator protein RepB.
杂乱的链球菌质粒pLS1编码5.1 kDa的RepA蛋白，该蛋白参与质粒拷贝数的调控。在枯草芽孢杆菌小细胞和大肠杆菌表达系统中均观察到RepA的合成。从该系统中纯化出了该蛋白，它似乎是由相同亚基组成的二聚体。已确定RepA的氨基酸序列。RepA具有许多DNA结合蛋白典型的α螺旋-转角-α螺旋基序，并且与许多阻遏物具有同源性，特别是与广宿主范围质粒RK2编码的TrfB阻遏物具有同源性。DNase I足迹分析表明，RepA的靶标位于repA和repB基因启动子区域。反式互补分析表明，在体内，RepA通过调节质粒拷贝数发挥阻遏物的作用。我们提出，RepA的调节作用是通过限制起始蛋白RepB的合成来实现的。
