Abstract
Deinococcus radiodurans is extremely resistant to ionizing radiation and has an exceptional ability to repair DNA damage caused by various DNA-damaging agents. D. radiodurans uses the same DNA-repair strategies as other prokaryotes, but certain proteins involved in the classical DNA repair machinery have characteristics different from their counterparts. RecG helicase, which unwinds a variety of branched DNA molecules, such as Holliday junctions (HJ) and D-loops, plays important roles in DNA repair, recombination, and replication. Primary sequence analysis of RecG from a number of bacterial species revealed that three amino acids (QPW) in the DNA-binding wedge domain (WD) are well-conserved across the Deinococcus RecG proteins. Interactions involving these conserved residues and DNA substrates were predicted in modeled domain structures of D. radiodurans RecG (DrRecG). Compared to the WD of Escherichia coli RecG protein (EcRecG) containing FSA amino acids corresponding to QPW in DrRecG, the HJ binding activity of DrRecG-WD was higher than that of EcRecG-WD. Reciprocal substitution of FSA and QPW increased and decreased the HJ binding activity of the mutant WDs, EcRecG-WDQPW, and DrRecG-WDFSA, respectively. Following γ-irradiation treatment, the reduced survival rate of DrRecG mutants (ΔrecG) was fully restored by the expression of DrRecG, but not by that of EcRecG. EcRecGQPW also enhanced γ-radioresistance of ΔrecG, whereas DrRecGFSA did not. ΔrecG cells complemented in trans by DrRecG and EcRecGQPW reconstituted an intact genome within 3 h post-irradiation, as did the wild-type strain, but ΔrecG with EcRecG and DrRecGFSA exhibited a delay in assembly of chromosomal fragments induced by γ-irradiation. These results suggested that the QPW residues facilitate the association of DrRecG with DNA junctions, thereby enhancing the DNA repair efficiency of DrRecG.
Highlights
Deinococcus radiodurans is well known for its extreme resistance to lethal doses of ionizing radiation (IR) and many other DNA damaging agents, including mitomycin C (MMC), UV-C radiation, and desiccation (Slade and Radman, 2011)
RecG proteins largely consist of an N-terminal wedge domain (WD) critical to DNA binding, helicase core domains, including seven motifs common to DNA helicases, and the signature RecG translocation in RecG (TRG) motif (Fairman-Williams et al, 2010)
Analysis of the genome sequence of D. radiodurans identifies the typical complement of prokaryotic DNA repair proteins, suggesting the possibility that D. radiodurans uses the same DNA-repair strategies as other prokaryotes, but it does so in a manner that is somehow much more effective than that observed in other species to retain the extraordinary tolerance to DNA damage (Battista et al, 1999; White et al, 1999)
Summary
Deinococcus radiodurans is well known for its extreme resistance to lethal doses of ionizing radiation (IR) and many other DNA damaging agents, including mitomycin C (MMC), UV-C radiation, and desiccation (Slade and Radman, 2011). This remarkable resistance is thought to be attributed to its highly efficient DNA repair capacity and various antioxidative systems (Lim et al, 2019). RecFOR-dependent DSB repair is initiated by unwinding duplex DNA, followed by DNA end resection that degrades the broken ends in the 5'–3' direction to obtain 3' single-stranded DNA (ssDNA) tails (Rocha et al, 2005)
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