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  The Crystal Structure of Exonuclease RecJ Bound to Mn2+ Ion Suggests How Its Characteristic Motifs Are Involved in Exonuclease Activity



All living cells have DNA repair and recombination systems for the maintenance of genomic integrity. RecJ is a 5' to 3' exonuclease specific for single-stranded DNA and involved in homologous recombination, base excision repair, and mismatch repair. RecJ has five characteristic motifs in its sequence; the proteins having these motifs are ubiquitous in archaea, prokaryotes, and higher eukaryotes and they form a large family of the predicted phosphoesterases (DHH family). We determined the structure of RecJ from Thermus thermophilus HB8 bound to Mn2+ essential for its activity by X-ray crystallography. RecJ has a novel fold, in which two domains are interconnected with a long helix to form a central groove. This groove is composed of conserved residues and positively charged, which may be involved in DNA binding. The width of the groove is too narrow to bind to double-stranded DNA, indicating the specificity for single-stranded DNA. Mn2+ is coordinated to the amino acid residues in the motifs characteristic to DHH the family. The structure of RecJ suggested the putative catalytic residues for its nuclease reaction. Mutation of these residues resulted in the loss or severe reduction of the nuclease activity. Based on these results, we proposed the mechanism of the nuclease reaction by RecJ.

*Reproduced with permission from Proc. Natl. Acad. Sci USA, 99, 5908-5912(2002)


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