Chromosome cohesion factor involved in sister chromatid cohesion and fidelity of chromosome transmission. Component of one of the cell nuclear antigen loader complexes, CTF18-replication factor C (CTF18-RFC), which consists of CTF18, CTF8, DCC1, RFC2, RFC3, RFC4 and RFC5. The CTF18-RFC complex binds to single-stranded and primed DNAs and has weak ATPase activity that is stimulated by the presence of primed DNA, replication protein A (RPA) and by proliferating cell nuclear antigen (PCNA). The CTF18-RFC complex catalyzes the ATP- dependent loading of PCNA onto primed and gapped DNA. Interacts with and stimulates DNA polymerase POLH. During DNA repair synthesis, involved in loading DNA polymerase POLE at the sites of local damage (PubMed:20227374). {ECO:0000269|PubMed:12766176, ECO:0000269|PubMed:12930902, ECO:0000269|PubMed:17545166, ECO:0000269|PubMed:20227374}. This is the function of Ensembl gene identifier ENSG00000127586 (CHTF18, chromosome transmission fidelity factor 18).