What is the name of the protein complex that loads PCNA onto DNA?

The protein complex that loads PCNA onto DNA is replication factor C, commonly abbreviated RFC. RFC is the eukaryotic clamp loader: it opens the PCNA ring and places it around DNA at a primer-template junction.

In the standard eukaryotic system, RFC is a heteropentamer made of five subunits, named RFC1 through RFC5. It recognizes the junction between a template strand and a newly synthesized primer, then uses ATP-driven conformational changes to load PCNA. Once PCNA is properly positioned, RFC releases it so a DNA polymerase can bind and extend the primer.

RFC is functionally comparable to bacterial clamp-loader complexes, although the proteins are not identical. A frequent mix-up is the MCM complex, which provides the replicative helicase, or the origin recognition complex, which helps identify replication origins. DNA polymerase epsilon synthesizes much of the leading strand; it does not load PCNA. RFC also contributes to DNA repair and checkpoint-related processes beyond ordinary chromosome duplication.