This protein is an auxiliary protein of DNA polymerase delta and is involved in the control of eukaryotic DNA replication by increasing the polymerase's processibility during elongation of the leading strand (PubMed:8663159). Involved in DNA repair (PubMed:16641370). Homotrimer (PubMed:9592143). Interacts with cdc24, rfc1, and rtf2 (PubMed:19416828, PubMed:9891039). Monoubiquitinated on Lys-164 by the rhp6/rhp18 complex upon DNA damage, and then polyubiquitinated through 'Lys-63'-linkage by ubc13/mms2 (PubMed:16641370). Ubiquitination contributes to efficient DNA replication in the absence of DNA damage (PubMed:28481910). Belongs to the PCNA family.