Involvement of Int _Tn916 Type Tyrosine Recombinase in Nucleoid Structure in <i>Deinococcus radiodurans</i>

Tyrosine recombinases (YRs) are widespread among prokaryotes and archaea, catalyzing site-specific DNA recombination reactions in a variety of cellular processes like chromosome dimer resolution, transfer of mobile genetic elements, and DNA insertion. Deinococcus radiodurans is a gram-positive bacterium which is highly resistant to ionizing radiation. This bacterium harbors a tightly condensed nucleoid containing polyploid, and multipartite genome. Deinococcal FtsK protein was earlier reported to stimulate site-specific recombination catalyzed by Escherichia coli YRs- XerC and XerD in vitro. The trans expression of Escherichia coli XerC and XerD proteins in D. radiodurans resulted in diffused nucleoids and sensitivity to gamma radiation compared to control cells indicative of the role of YRs in nucleoid morphology. Protein-protein interaction studies revealed the interaction of putative deinococcal YRs- Dr0513 (Int_Tn916 type YR), DrA0155 and DrB0104 with DrFtsK. Overexpression of these putative YRs in E. coli resulted in filamentous cells with partitioned nucleoids. D. radiodurans Δdr0513 single mutant as well as Δdr0513ΔftsK double mutant cells exhibited altered nucleoid morphologies. The Δdr0513ΔftsK double mutant had slow growth rates both under normal and post gamma radiation recovery periods. Mislocalization of the HU protein on the nucleoid was also observed in the double mutant cells. Further, in vivo recombination experiments performed with a reporter plasmid containing E. coli dif sequence revealed that Dr0513 could perform site-specific recombination in the ∆xerC E. coli strain. These results functionally validate the role of uncharacterized Dr0513 protein as tyrosine recombinase in D. radiodurans, with a probable role in nucleoid compaction and genome maintenance in conjunction with DrFtsK.