Ausiannikava Darya, Allers Thorsten
School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK;.
Genes (Basel). 2017 Jan 31;8(2):56. doi: 10.3390/genes8020056.
DNA replication is arguably the most fundamental biological process. On account of their shared evolutionary ancestry, the replication machinery found in archaea is similar to that found in eukaryotes. DNA replication is initiated at origins and is highly conserved in eukaryotes, but our limited understanding of archaea has uncovered a wide diversity of replication initiation mechanisms. Archaeal origins are sequence-based, as in bacteria, but are bound by initiator proteins that share homology with the eukaryotic origin recognition complex subunit Orc1 and helicase loader Cdc6). Unlike bacteria, archaea may have multiple origins per chromosome and multiple Orc1/Cdc6 initiator proteins. There is no consensus on how these archaeal origins are recognised- some are bound by a single Orc1/Cdc6 protein while others require a multi- Orc1/Cdc6 complex. Many archaeal genomes consist of multiple parts-the main chromosome plus several megaplasmids-and in polyploid species these parts are present in multiple copies. This poses a challenge to the regulation of DNA replication. However, one archaeal species (Haloferax volcanii) can survive without replication origins; instead, it uses homologous recombination as an alternative mechanism of initiation. This diversity in DNA replication initiation is all the more remarkable for having been discovered in only three groups of archaea where in vivo studies are possible.
DNA复制可以说是最基本的生物学过程。由于古菌与真核生物有着共同的进化起源，古菌中发现的复制机制与真核生物中的相似。DNA复制在起始点开始，在真核生物中高度保守，但我们对古菌的有限了解揭示了多种复制起始机制。古菌的起始点像细菌一样基于序列，但由与真核生物起源识别复合物亚基Orc1和解旋酶装载蛋白Cdc6具有同源性的起始蛋白结合。与细菌不同，古菌每条染色体可能有多个起始点和多个Orc1/Cdc6起始蛋白。关于如何识别这些古菌起始点尚无共识——有些由单个Orc1/Cdc6蛋白结合，而另一些则需要多Orc1/Cdc6复合物。许多古菌基因组由多个部分组成——主染色体加上几个大质粒——在多倍体物种中，这些部分以多个拷贝存在。这对DNA复制的调控提出了挑战。然而，一种古菌（嗜盐嗜碱菌）在没有复制起始点的情况下也能存活；相反，它利用同源重组作为起始的替代机制。DNA复制起始的这种多样性在仅三组可进行体内研究的古菌中被发现，这一点尤为显著。
