CRYSTAL-STRUCTURE OF THE EUKARYOTIC DNA-POLYMERASE PROCESSIVITY FACTOR PCNA

The crystal structure of the processivity factor required by eukaryoti c DNA polymerase delta, proliferating cell nuclear antigen (PCNA) from S. cerevisiae, has been determined at 2.3 Angstrom resolution. Three PCNA molecules, each containing two topologically identical domains, a re tightly associated to form a closed ring. The dimensions and electr ostatic properties of the ring suggest that PCNA encircles duplex DNA, providing a DNA-bound platform for the attachment of the polymerase. The trimeric PCNA ring is strikingly similar to the dimeric ring forme d by the beta subunit (processivity factor) of E. coli DNA polymerase III holoenzyme, with which it shares no significant sequence identity. This structural correspondence further substantiates the mechanistic connection between eukaryotic and prokaryotic DNA replication that has been suggested on biochemical grounds.