Deinococcus radiodurans, an extremophile, resistant to many abiotic stresses including ionizing radiation, has 2 type I topoisomerases (drTopo IA and drTopo IB) and one type II topoisomerase (DNA gyrase). The role of drTopo IB in guanine quadruplex DNA (G4 DNA) metabolism was demonstrated earlier in vitro. Here, we report that D. radiodurans cells lacking drTopo IB (ΔtopoIB) show sensitivity to G4 DNA binding drug (NMM) under normal growth conditions. The activity of G4 motif containing promoters like mutL and recQ was reduced in the presence of NMM in mutant cells. In mutant, the percentage of anucleate cells was more while the copy number of genome elements were less as compared to wild type. Protein-protein interaction studies showed that drTopo IB interacts with genome segregation and DNA replication initiation (DnaA) proteins. The typical patterns of cellular localization of GFP-PprA were affected in the mutant cells. Microscopic examination of D. radiodurans cells expressing drTopo IB-RFP showed its localization on nucleoid forming a streak parallel to the old division septum and perpendicular to newly formed septum. These results together suggest the role of drTopo IB in genome maintenance in this bacterium.

嗜热绝热球菌Deinococcus radiodurans对许多非生物胁迫（包括电离辐射）具有抵抗力，它具有2种I型拓扑异构酶（drTopo IA和drTopo IB）和一种II型拓扑异构酶（DNA旋转酶）。drTopo IB在鸟嘌呤四链体DNA（G4 DNA）代谢中的作用已在体外得到证实。在这里，我们报告缺乏正常的生长条件下缺乏drTopo IB（ΔtopoIB）的D. radiodurans细胞显示出对G4 DNA结合药物（NMM）的敏感性。包含mutL和recQ等启动子的G4基序的活性在突变细胞中存在NMM的情况下，其减少。与野生型相比，在突变体中，无核细胞百分比更高，而基因组元件的拷贝数则更少。蛋白质-蛋白质相互作用研究表明，drTopo IB与基因组分离和DNA复制起始（DnaA）蛋白质相互作用。GFP-PprA的典型细胞定位模式在突变细胞中受到影响。显微镜下观察表达drTopo IB-RFP的放射线虫的细胞，发现其定位在类核苷酸上，形成平行于旧分隔隔膜并垂直于新形成的隔膜的条纹。这些结果共同表明drTopo IB在该细菌的基因组维持中的作用。