1
Department of Structural Biology, Biomolecular Engineering Research Institute (BERI), 6-2-3 Furuedai, Suita, Osaka
565-0874, Japan.
2
Laboratory of Protein Chemistry and Engineering, Faculty of Agriculture, Kyushu University, Hakozaki, Higash-ku, Fukuoka-shi, Fukuoka
812-8581, Japan.
DNA polymerase requires two processing factors, sliding clamps and clamp loaders, to direct rapid and accurate duplication of genomic DNA. In eukaryotes, proliferating cell nuclear antigen (PCNA), the ring-shaped sliding clamp, encircles double-stranded DNA within its central hole and tethers the DNA polymerases onto DNA. Replication factor C (RFC) acts as the clamp loader, which correctly installs the sliding clamp onto DNA strands in an ATP-dependent manner. Here we report the three-dimensional structure of an archaeal clamp-loading complex (RFC−PCNA−DNA) determined by single-particle EM. The three-dimensional structure of the complex, reconstituted in vitro using a nonhydrolyzable ATP analog, reveals two components, a closed ring and a horseshoe-shaped element, which correspond to PCNA and RFC, respectively. The atomic structure of PCNA fits well into the closed ring, suggesting that this ternary complex represents a state just after the PCNA ring has closed to encircle the DNA duplex.
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