Alternative titles; symbols
HGNC Approved Gene Symbol: RFC2
Cytogenetic location: 7q11.23 Genomic coordinates (GRCh38): 7:74,231,502-74,254,399 (from NCBI)
Human replication factor C (RFC), also called activator-1, is a multimeric primer-recognition protein consisting of 5 distinct subunits of 145, 40, 38, 37, and 36.5 kD. Human RFC was purified from extracts of HeLa cells as a host factor essential for the in vitro replication of simian virus 40 (SV40) DNA (Okumura et al., 1995). RFC, in the presence of ATP, assembles proliferating-cell nuclear antigen (PCNA; 176740) and DNA polymerase-delta (174761) or polymerase-epsilon (174762) on primed DNA templates. The complex of primed DNA-RFC-PCNA-DNA polymerase, when supplemented with dNTPs, results in the efficient elongation of DNA in the presence of human single-stranded DNA binding protein. Studies with the complete 5-subunit holoenzyme indicated that the large subunit binds to DNA and the 40-kD subunit binds ATP. The other subunits may play discrete roles in the elongation process catalyzed by polymerase. The subunit genes are numbered in sequence of decreasing molecular weight: RFC1 (102579), RFC2, RFC3 (600405), RFC4 (102577), and RFC5 (600407).
Wang et al. (2000) used immunoprecipitation and mass spectrometry analyses to identify BRCA1 (113705)-associated proteins. They found that BRCA1 is part of a large multisubunit protein complex of tumor suppressors, DNA damage sensors, and signal transducers. They named this complex BASC, for 'BRCA1-associated genome surveillance complex.' Among the DNA repair proteins identified in the complex were ATM (607585), BLM (604610), MSH2 (609309), MSH6 (600678), MLH1 (120436), the RAD50 (604040)-MRE11 (600814)-NBS1 (602667) complex, and the RFC1-RFC2-RFC4 complex. Wang et al. (2000) suggested that BASC may serve as a sensor of abnormal DNA structures and/or as a regulator of the postreplication repair process.
Using affinity chromatography and coexpression and immunoprecipitation analysis, Ohta et al. (2002) showed that CHL12 (CHTF18; 613201) did not interact directly with PCNA, but it formed a pentameric complex with RFC2, RFC3, RFC4, and RFC5, and this complex bound PCNA.
By immunoprecipitating proteins that associated with epitope-tagged CHTF18 from human 293T cells, Bermudez et al. (2003) determined that CHTF18 was a component of a 7-subunit cohesion-RFC complex, which they called CTF18-RFC. This complex also included stoichiometric amounts of DCC1 (DSCC1; 613203), CTF8 (CHTF8; 613202), and the RFC2-5 subunits. These 7 subunits also assembled into a 5-subunit complex of CTF18, RFC2-5, and a DCC1-CTF8 dimer. Assembly of in vitro-translated components showed that CTF8 bound CTF18 in the 5-subunit complex, but not CTF18 alone, and the addition of DCC1 stabilized the completed 7-subunit CTF18-RFC complex. Both the 5- and 7-subunit CTF18-RFC complexes showed weak DNA-dependent ATPase activity that was stimulated by primed single-stranded DNA. Maximal stimulation of ssDNA-dependent ATPase activity required addition of RPA (see 179837) and PCNA. Both the 7- and 5-subunit CTF18-RFC complexes loaded PCNA onto primed and gapped circular DNA, but not onto single-stranded circular DNA or onto singly nicked circular DNA. CTF18-RFC also released PCNA that was preloaded onto DNA in an ATP-dependent manner. Both CTF18-RFC complexes supported PCNA-dependent DNA polymerase delta (see 174761)-catalyzed elongation of singly primed DNA. The CTF18 subunit also showed weak interaction with the cohesin subunits SMC1 (see 300040) and SCC1 (RAD21; 606462). Bermudez et al. (2003) concluded that the CTF18-RFC complex functions as a PCNA clamp loader and may link sister chromatid cohesion with DNA replication.
Through single-molecule analysis, Terret et al. (2009) demonstrated that a replication complex, the RFC-CTF18 clamp loader, controls the velocity spacing and restart activity of replication forks in human cells and is required for robust acetylation of cohesin's SMC3 subunit (606062) and sister chromatid cohesion. Unexpectedly, Terret et al. (2009) discovered that cohesin acetylation itself is a central determinant of fork processivity, as slow-moving replication forks were found in cells lacking the Eco1-related acetyltransferases ESCO1 (609674) or ESCO2 (609353) (including those derived from Roberts syndrome (268300) patients, in whom ESCO2 is biallelically mutated), and in cells expressing a form of SMC3 that cannot be acetylated. This defect was a consequence of cohesin's hyperstable interaction with 2 regulatory cofactors, WAPL (610754) and PDS5A (613200); removal of either cofactor allowed forks to progress rapidly without ESCO1, ESCO2, or RFC-CTF18. Terret et al. (2009) concluded that their results showed a novel mechanism for clamp loader-dependent fork progression, mediated by the posttranslational modification and structural remodeling of the cohesin ring. Loss of this regulatory mechanism leads to the spontaneous accrual of DNA damage and may contribute to the abnormalities of the Roberts syndrome cohesinopathy.
Crystal Structure
Bowman et al. (2004) reported the crystal structure of the 5-protein clamp loader complex (replication factor-C, RFC) of the yeast S. cerevisiae, bound to the sliding clamp (PCNA). Tight interfacial coordination of the ATP analog ATP-gamma-S by RFC resulted in a spiral arrangement of the ATPase domains of the clamp loader above the PCNA ring. Placement of a model for primed DNA within the central hole of PCNA revealed a striking correspondence between the RFC spiral and the grooves of the DNA double helix. Bowman et al. (2004) concluded that this model, in which the clamp loader complex locks into primed DNA in a screwcap-like arrangement, provides a simple explanation for the process by which the engagement of primer-template junctions by the RFC:PCNA complex results in ATP hydrolysis and release of the sliding clamp on DNA.
Using both PCR amplification of DNAs from a panel of somatic hybrids and fluorescence in situ hybridization (FISH), Okumura et al. (1995) mapped the RFC2 gene to 7q11.23; the RFC3 gene to 13q12.3-q13; the RFC4 gene to 3q27; and the RFC5 gene to 12q24.2-q24.3. RFC1 had been mapped to 4p14-p13.
By analysis of somatic cell hybrids and FISH, Peoples et al. (1996) showed that RFC2 maps within the 7q11.23 Williams syndrome deletion (WBS; 194050).
Peoples et al. (1996) showed that the RFC2 gene was deleted in each of 18 patients with Williams syndrome studied. They postulated a mechanism of haploinsufficiency wherein deletion of RFC2 subunits on one chromosome may lead to reduced efficiency of DNA replication, which could account for growth deficiency as well as developmental disturbances.
Venclovas et al. (2002) stated that the nomenclature for the RFC subunits was developed independently for human and budding yeast, and therefore, sometimes causes confusion as to which RFC subunit in yeast corresponds to that in human. The correspondence between human and yeast nomenclatures is as follows: RFC1(p145) to Rfc1, RFC2(p40) to Rfc4, RFC3(p38) to Rfc5, RFC4(p37) to Rfc2, and RFC5(p36) to Rfc3.
Bermudez, V. P., Maniwa, Y., Tappin, I., Ozato, K., Yokomori, K., Hurwitz, J. The alternative Ctf18-Dcc1-Ctf8-replication factor C complex required for sister chromatid cohesion loads proliferating cell nuclear antigen onto DNA. Proc. Nat. Acad. Sci. 100: 10237-10242, 2003. [PubMed: 12930902] [Full Text: https://doi.org/10.1073/pnas.1434308100]
Bowman, G. D., O'Donnell, M., Kuriyan, J. Structural analysis of a eukaryotic sliding DNA clamp-clamp loader complex. Nature 429: 724-730, 2004. [PubMed: 15201901] [Full Text: https://doi.org/10.1038/nature02585]
Ohta, S., Shiomi, Y., Sugimoto, K., Obuse, C., Tsurimoto, T. A proteomics approach to identify proliferating cell nuclear antigen (PCNA)-binding proteins in human cell lysates. J. Biol. Chem. 277: 40362-40367, 2002. [PubMed: 12171929] [Full Text: https://doi.org/10.1074/jbc.M206194200]
Okumura, K., Nogami, M., Taguchi, H., Dean, F. B., Chen, M., Pan, Z.-Q., Hurwitz, J., Shiratori, A., Murakami, Y., Ozawa, K., Eki, T. Assignment of the 36.5-kDa (RFC5), 37-kDa (RFC4), 38-kDa (RFC3), and 40-kDa (RFC2) subunit genes of human replication factor C to chromosome bands 12q24.2-q24.3, 3q27, 13q12.3-q13, and 7q11.23. Genomics 25: 274-278, 1995. [PubMed: 7774928] [Full Text: https://doi.org/10.1016/0888-7543(95)80135-9]
Peoples, R., Perez-Jurado, L., Wang, Y.-K., Kaplan, P., Francke, U. The gene for replication factor C subunit 2 (RFC2) is within the 7q11.23 Williams syndrome deletion. (Letter) Am. J. Hum. Genet. 58: 1370-1373, 1996. [PubMed: 8651315]
Terret, M.-E., Sherwood, R., Rahman, S., Qin, J., Jallepalli, P. V. Cohesin acetylation speeds the replication fork. Nature 462: 231-234, 2009. [PubMed: 19907496] [Full Text: https://doi.org/10.1038/nature08550]
Venclovas, C., Colvin, M. E., Thelen, M. P. Molecular modeling-based analysis of interactions in the RFC-dependent clamp-loading process. Protein Sci. 11: 2403-2416, 2002. [PubMed: 12237462] [Full Text: https://doi.org/10.1110/ps.0214302]
Wang, Y., Cortez, D., Yazdi, P., Neff, N., Elledge, S. J., Qin, J. BASC, a super complex of BRCA1-associated proteins involved in the recognition and repair of aberrant DNA structures. Genes Dev. 14: 927-939, 2000. [PubMed: 10783165]