Christensen B B, Atlung T, Hansen F G
Department of Microbiology, The Technical University of Denmark, DK-2800 Lyngby, Denmark.
J Bacteriol. 1999 May;181(9):2683-8. doi: 10.1128/JB.181.9.2683-2688.1999.
The binding of DnaA protein to its DNA binding sites-DnaA boxes-in the chromosomal oriC region is essential for initiation of chromosome replication. In this report, we show that additional DnaA boxes affect chromosome initiation control, i.e., increase the initiation mass. The cellular DnaA box concentration was increased by introducing pBR322-derived plasmids carrying DnaA boxes from the oriC region into Escherichia coli and by growing the strains at different generation times to obtain different plasmid copy numbers. In fast-growing cells, where the DnaA box plasmid copy number per oriC locus was low, the presence of extra DnaA boxes caused only a moderate increase in the initiation mass. In slowly growing cells, where the DnaA box plasmid copy number per oriC locus was higher, we observed more pronounced increases in the initiation mass. Our data clearly show that the presence of extra DnaA boxes increases the initiation mass, supporting the idea that the initiation mass is determined by the normal complement of DnaA protein binding sites in E. coli cells.
DnaA蛋白与染色体oriC区域的DNA结合位点——DnaA框——的结合对于染色体复制的起始至关重要。在本报告中，我们表明额外的DnaA框会影响染色体起始控制，即增加起始质量。通过将携带oriC区域DnaA框的pBR322衍生质粒导入大肠杆菌，并在不同世代时间培养菌株以获得不同的质粒拷贝数，来提高细胞中DnaA框的浓度。在快速生长的细胞中，每个oriC位点的DnaA框质粒拷贝数较低，额外DnaA框的存在仅导致起始质量适度增加。在缓慢生长的细胞中，每个oriC位点的DnaA框质粒拷贝数较高，我们观察到起始质量有更明显的增加。我们的数据清楚地表明，额外DnaA框的存在会增加起始质量，支持起始质量由大肠杆菌细胞中DnaA蛋白结合位点的正常互补决定这一观点。
