Villarroya M, Pérez-Roger I, Macián F, Armengod M E
Instituto de Investigaciones Citológicas, Fundación Valenciana de Investigaciones Biomedicas, Valencia 46010, Spain.
EMBO J. 1998 Mar 16;17(6):1829-37. doi: 10.1093/emboj/17.6.1829.
The beta subunit of DNA polymerase III holoenzyme, the Escherichia coli chromosomal replicase, is a sliding DNA clamp responsible for tethering the polymerase to DNA and endowing it with high processivity. The gene encoding beta, dnaN, maps between dnaA and recF, which are involved in initiation of DNA replication at oriC and resumption of DNA replication at disrupted replication forks, respectively. In exponentially growing cells, dnaN and recF are expressed predominantly from the dnaA promoters. However, we have found that stationary phase induction of the dnaN promoters drastically changes the expression pattern of the dnaA operon genes. As a striking consequence, synthesis of the beta subunit and RecF protein increases when cell metabolism is slowing down. Such an induction is dependent on the stationary phase sigma factor, RpoS, although the accumulation of this factor alone is not sufficient to activate the dnaN promoters. These promoters are located in DNA regions without static bending, and the -35 hexamer element is essential for their RpoS-dependent induction. Our results suggest that stationary phase-dependent mechanisms have evolved in order to coordinate expression of dnaN and recF independently of the dnaA regulatory region. These mechanisms might be part of a developmental programme aimed at maintaining DNA integrity under stress conditions.
DNA聚合酶III全酶的β亚基是大肠杆菌染色体复制酶，它是一种滑动DNA夹，负责将聚合酶与DNA相连并赋予其高持续性。编码β的基因dnaN定位于dnaA和recF之间，它们分别参与oriC处的DNA复制起始和中断复制叉处的DNA复制恢复。在指数生长的细胞中，dnaN和recF主要从dnaA启动子表达。然而，我们发现dnaN启动子的稳定期诱导会极大地改变dnaA操纵子基因的表达模式。一个显著的结果是，当细胞代谢减缓时，β亚基和RecF蛋白的合成增加。这种诱导依赖于稳定期σ因子RpoS，尽管仅该因子的积累不足以激活dnaN启动子。这些启动子位于没有静态弯曲的DNA区域，并且-35六聚体元件对于它们依赖RpoS的诱导至关重要。我们的结果表明，已经进化出稳定期依赖性机制，以便独立于dnaA调控区域来协调dnaN和recF的表达。这些机制可能是旨在在应激条件下维持DNA完整性的发育程序的一部分。
