Boonsombat Ruethairat, Yeh Su-Ping, Milne Amy, Sandler Steven J
Department of Microbiology, Morrill Science Center IV N203, University of Massachusetts at Amherst, Amherst, MA 01003, USA.
Mol Microbiol. 2006 May;60(4):973-83. doi: 10.1111/j.1365-2958.2006.05147.x.
The loading of a replisome in prokaryotic and eukaryotic cells at an origin of DNA replication and during replication restart is a highly ordered and regulated process. During replication restart in Escherichia coli, the PriA, PriB, PriC, DnaT and Rep proteins form multiple pathways that bind to repaired replication forks. These complexes are then recognized by DnaC as sites to load DnaB, the replicative helicase. Several dnaC mutations have been isolated that suppress phenotypes of some replication restart mutants. A new dnaC mutation (dnaC824) is reported here that efficiently suppresses priB rep mutant phenotypes. Furthermore, it is shown that dnaC824 will suppress phenotypes of priB priA300, rep priA300 and priB priC strains. Unlike other dnaC suppressors, it can only weakly suppress the absence of priA. Others have reported a different type of dnaC mutation, dnaC1331, is able to mimic priB mutant phenotypes. This is supported herein by showing that like dnaC1331, a priB mutation is synthetically lethal with a dam mutation and this can be rescued by a mutH mutation. Furthermore, priB dam lethality can also be suppressed by dnaC824. Like a priB mutation, a dnaC1331 mutation causes a priA2::kan-like phenotype when combined with priA300. Lastly, we show that dnaC824 is dominant to wild type and that dnaC1331 is recessive to wild type. Several models are discussed for the action of these mutant dnaC proteins in replication restart.
在原核细胞和真核细胞中，复制体在DNA复制起点以及复制重新启动过程中的装载是一个高度有序且受到调控的过程。在大肠杆菌的复制重新启动过程中，PriA、PriB、PriC、DnaT和Rep蛋白形成多条与修复后的复制叉结合的途径。然后这些复合物被DnaC识别为装载复制解旋酶DnaB的位点。已经分离出几种dnaC突变体，它们能抑制一些复制重新启动突变体的表型。本文报道了一种新的dnaC突变体（dnaC824），它能有效抑制priB rep突变体的表型。此外，研究表明dnaC824能抑制priB priA300、rep priA300和priB priC菌株的表型。与其他dnaC抑制子不同，它只能微弱地抑制priA缺失的情况。其他人报道过一种不同类型的dnaC突变体dnaC1331，它能够模拟priB突变体的表型。本文通过如下研究支持了这一点：与dnaC1331一样，priB突变与dam突变是合成致死的，而这可以通过mutH突变得到挽救。此外，priB dam致死性也能被dnaC824抑制。与priB突变一样，dnaC1331突变与priA300组合时会导致priA2::kan样的表型。最后，我们表明dnaC824对野生型是显性的，而dnaC1331对野生型是隐性的。文中讨论了这些突变的dnaC蛋白在复制重新启动中的作用的几种模型。
