Williams Jessica S, Clausen Anders R, Lujan Scott A, Marjavaara Lisette, Clark Alan B, Burgers Peter M, Chabes Andrei, Kunkel Thomas A
Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA.
Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden.
Nat Struct Mol Biol. 2015 Apr;22(4):291-7. doi: 10.1038/nsmb.2989. Epub 2015 Mar 9.
Ribonucleotides incorporated during DNA replication are removed by RNase H2-dependent ribonucleotide excision repair (RER). In RER-defective yeast, topoisomerase 1 (Top1) incises DNA at unrepaired ribonucleotides, initiating their removal, but this is accompanied by RNA-DNA-damage phenotypes. Here we show that these phenotypes are incurred by a high level of ribonucleotides incorporated by a leading strand-replicase variant, DNA polymerase (Pol) ɛ, but not by orthologous variants of the lagging-strand replicases, Pols α or δ. Moreover, loss of both RNases H1 and H2 is lethal in combination with increased ribonucleotide incorporation by Pol ɛ but not by Pols α or δ. Several explanations for this asymmetry are considered, including the idea that Top1 incision at ribonucleotides relieves torsional stress in the nascent leading strand but not in the nascent lagging strand, in which preexisting nicks prevent the accumulation of superhelical tension.
在DNA复制过程中掺入的核糖核苷酸通过核糖核酸酶H2依赖性核糖核苷酸切除修复（RER）被去除。在RER缺陷的酵母中，拓扑异构酶1（Top1）在未修复的核糖核苷酸处切割DNA，启动其去除，但这伴随着RNA-DNA损伤表型。我们在此表明，这些表型是由前导链复制酶变体DNA聚合酶（Pol）ɛ掺入的高水平核糖核苷酸引起的，而不是由滞后链复制酶Polα或Polδ的直系同源变体引起的。此外，核糖核酸酶H1和H2的缺失与Polɛ而非Polα或Polδ增加的核糖核苷酸掺入相结合是致命的。我们考虑了这种不对称性的几种解释，包括核糖核苷酸处的Top1切割缓解新生前导链中的扭转应力但不缓解新生滞后链中的扭转应力这一观点，在新生滞后链中，预先存在的切口可防止超螺旋张力的积累。
