Crystal structure of an 82-nucleotide RNA-DNA complex formed by the 10-23 DNA enzyme

The structure of a large nucleic acid complex formed by the 10-23 DNA enzym e bound to an RNA substrate was determined by X-ray diffraction at 3.0 Angs trom resolution. The 82-nucleotide complex contains two strands of DNA and two strands of RNA that form five double-helical domains. The spatial arran gement of these helices is maintained by two four-way junctions that exhibi t extensive base-stacking interactions and sharp turns of the phosphodieste r backbone stabilized by metal ions coordinated to nucleotides at these jun ctions. Although it is unlikely that the structure corresponds to the catal ytically active conformation of the enzyme, it represents a novel nucleic a cid fold with implications for the Holliday junction structure.