Topoisomerase IB interacts with genome segregation proteins and is involved in multipartite genome maintenance inDeinococcus radiodurans

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 shown in vitro . Here we report that D. radiodurans cells lacking drTopo IB (Δ topoIB ) 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 cells, the percentage of anucleated cells was more while the ploidy numbers 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.