Biochemical characterization and functional insights into DNA substrate-specific activities of a unique radiation-inducible DR1143 protein from Deinococcus radiodurans

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The highly radiation-resistant bacterium Deinococcus radiodurans R1 employs various pathways to respond to radiation and other genotoxic stresses, involving the upregulation of several genes. Despite decades of study, the functions of many D. radiodurans genes remain unknown. Among them, the DR1143 gene has been reported transiently induced during the early phase of post-irradiation recovery. The DR1143 protein has been detected in the interactomes of key DNA repair proteins, including Ssb, RecA, and DdrB, suggesting its involvement in DNA repair processes. Our study revealed that DR1143 exhibits structural similarity to structural maintenance proteins (SMC) and exists as a hexamer in its soluble form. The protein showed a preference for binding longer DNA molecules (≥2 kb) and interacted differentially with various DNA forms. It bound single-stranded DNA (ssDNA) with high affinity, compacted, and protected it, indicating a potential role in safeguarding ssDNA during repair. DR1143 also created a single-strand nick in circular double-stranded DNA (dsDNA) while simply binding to linear dsDNA. Its nickase activity likely facilitates DNA end resection and relaxation, a critical step in repair processes. Localization studies using GFP-tagged DR1143 showed its accumulation at cell poles in both Escherichia coli and D. radiodurans, hinting at a functional role in specific subcellular compartments.