Interaction between the replicational initiator DnaA and the DNA polymerase components

在大肠在大肠杆菌中，DnaA蛋白与染色体复制起点（oriC）形成复合物。在这个复合体中，DnaA打开双链DNA。DnaA蛋白的这种起始活性依赖于ATP结合。在产生的单链区域上，DNA聚合酶III，染色体的复制酶，是loaded.We最近发现，结合到DnaA的ATP的水解是通过与DNA聚合酶III的滑动夹和部分纯化的ShakespeB蛋白组分的相互作用而加速的。滑动夹是环状构型，其由复制酶的β亚基的二聚体组成，并将DNA链拴系到复制酶。通过该反应，迅速产生ADP形式的DnaA，其为引发的无活性形式。我们将该系统命名为RIDA，即Regulatory Inactivation of DnaA，并建议RIDA是防止额外启动的主要系统，以维持每个染色体每个细胞周期仅启动一次的频率。事实上，某些对RIDA不敏感的DnaA突变蛋白导致染色体复制的过度起始。此外，我们有体内证据表明RIDA依赖于DNA复制所必需的基因。在随机分裂的细胞中，ATP形式的DnaA含量占ATP/ADP结合的DnaA总分子的15 - 30%，当DNA复制所需的基因失活时，ATP-DnaA水平增加到80%。这些结果表明，ATP-DnaA水平在依赖于DNA复制的细胞周期中受到抑制，这可能是控制染色体复制起始周期的关键事件。

In E. coli, DnaA protein forms a complex with the chromosomal replication origin (oriC). In this complex, DnaA opens the duplex DNA. This initiation activity of DnaA protein depends on ATP binding. On the generated single stranded region, DNA polymerase III, the replicase of chromosome, is loaded.We recently revealed that the hydrolysis of ATP bound to DnaA is accelerated by interaction with the sliding clamp of DNA polymerase III and a partially purified IdaB protein fraction. The sliding clamp is a ring-like configuration that is comprised from a dimer of the β subunit of the replicase and tethers DNA strand to the replicase. By this reaction, the ADP form of DnaA, an inactive form for initiation, is rapidly generated. We named this system RIDA for Regulatory Inactivation of DnaA, and suggested that RIDA is a main system to prevent extra initiations for maintaining the frequency of initiation only once per chromosome per cell cycle. Indeed, certain DnaA mutant proteins that are insensitive to a RIDA causes overinitiation of chromosomal replication. Moreover, we had in vivo evidence that RIDA depends on genes necessary for DNA replication. Content of the ATP form of DnaA in randomly dividing cells is 15 - 30% of total ATP/ADP-bound DnaA molecules, and when genes required for DNA replication were inactivated, the ATP-DnaA level increased up to 80%. These results suggest that the ATP-DnaA level is restrained during the cell cycle depending on DNA replication, which may be a key event to control the initiation cycle of chromosomal replication.