Alternative titles; symbols
HGNC Approved Gene Symbol: FANCI
Cytogenetic location: 15q26.1 Genomic coordinates (GRCh38): 15:89,243,979-89,317,259 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 15q26.1 | Fanconi anemia, complementation group I | 609053 | Autosomal recessive | 3 |
FANCI, a monoubiquitinated paralog of FANCD2 (227646), belongs to the Fanconi anemia (FA; see 227650) DNA interstrand cross-link repair pathway and is required for resistance to mitomycin C (Dorsman et al., 2007; Sims et al., 2007; Smogorzewska et al., 2007).
By screening a fetal brain cDNA library for cDNAs encoding large proteins, Nagase et al. (2001) cloned FANCI, which they called KIAA1794. The predicted protein contains 802 amino acids. RT-PCR ELISA detected moderate expression in testis and fetal liver and low expression in lung, liver, spleen, ovary, and adult and fetal brain. Expression was very low or undetectable in all other tissues tested. Expression was low in all specific brain regions examined, with slightly higher expression in cerebellum.
By linkage and bioinformatic analyses to identify the gene underlying FA complementation group I (609053), Dorsman et al. (2007) identified FANCI. The predicted FANCI protein contains 1,328 amino acids and has a calculated molecular mass of 146 kD. It has 3 nuclear localization signals and 3 ATM (607585)/ATR (601215) phosphorylation motifs. Western blot analysis revealed a 150-kD endogenous FANCI protein in lymphoblasts.
By searching databases for homologs of FANCD2, Sims et al. (2007) identified FANCI. Like FANCD2, FANCI contains a conserved monoubiquitination site, and the 2 proteins share about 40% similarity in the region surrounding the site.
Using a proteomic screen to identify ATM and ATR kinase substrates and a DNA damage sensitivity screen, followed by screening a lymphocyte cDNA library, Smogorzewska et al. (2007) cloned FANCI. FANCI contains 3 phosphorylation sites and a monoubiquitination site, lys523, homologous to the lys561 monoubiquitination site of FANCD2.
Dorsman et al. (2007) found that knockdown of FANCI expression by small interfering RNA (siRNA) in HeLa cells caused excessive chromosomal breakage induced by mitomycin C, a hallmark of FA cells.
Sims et al. (2007) found that FANCI was monoubiquitinated in a FANCD2-dependent manner and localized to nuclear foci following treatment of HeLa cells with DNA-damaging agents. Cell fractionation and immunoblot analysis showed that most monoubiquitinated FANCI was associated with chromatin in the nuclear fraction. Treatment of HeLa cells with siRNA to FANCI or FANCD2 resulted in sensitivity to mitomycin C. Sims et al. (2007) concluded that FANCI behaves as a functional homolog of FANCD2 in the coordination and repair of DNA cross-links.
Smogorzewska et al. (2007) found that treatment of U2OS cells with siRNA against FANCI abrogated the G2/M cell cycle checkpoint. FANCI localized to damage-induced foci in multiple cell types, and FANCI formed a complex with FANCD2 that was required for localization of FANCD2 to damage-induced foci. Mitomycin C treatment induced monoubiquitination of FANCI at lys523, and monoubiquitination of FANCI in the absence of DNA damage was also detectable during S phase. Mutation analysis showed that lys523 was critical for FANCI monoubiquitination. Ubiquitination of FANCI was dependent on FANCA (607139), and FANCI and FANCD2 showed reciprocal ubiquitination dependencies. Smogorzewska et al. (2007) concluded that FANCI is a FANCD2 paralog required for DNA cross-link repair, that it is monoubiquitinated, and that FANCI and FANCD2 form an interdependent complex required for ubiquitination and chromatin association.
Knipscheer et al. (2009) used a cell-free system to demonstrate that FANCI-FANCD2 (227646) is required for replication-coupled interstrand crosslink repair in S phase. Removal of FANCD2 from extracts inhibited both nucleolytic incisions near the interstrand crosslink and translesion DNA synthesis past the lesion. Reversal of these defects required ubiquitylated FANCI-FANCD2. Knipscheer et al. (2009) concluded that multiple steps of the essential S phase interstrand crosslink repair mechanism fail when the Fanconi anemia pathway is compromised.
A central event in the Fanconi pathway is monoubiquitylation of the FANCI-FANCD2 protein complex. Liu et al. (2010) characterized the Fanconi anemia-associated nuclease FAN1 (613534), which promotes interstrand crosslink repair in a manner strictly dependent on its ability to accumulate at or near sites of DNA damage and that relies on monoubiquitylation of the FANCI-FAND2 complex. Liu et al. (2010) concluded that the monoubiquitylated complex recruits the downstream repair protein FAN1 and facilitates repair of DNA interstrand crosslinks.
Long et al. (2011) reported that the broken sister chromatid generated by a DNA double-strand break in Xenopus extracts is repaired via RAD51 (179617)-dependent strand invasion into the regenerated sister. Recombination acts downstream of FANCI-FANCD2 (613984), yet RAD51 binds interstrand crosslinks-stalled replication forks independently of FANCI and FANC2 and before double-strand break formation. Long et al. (2011) concluded that their results elucidated the functional link between the Fanconi anemia pathway and the recombination machinery during interstrand crosslink repair. In addition, their results demonstrated the complete repair of a double-strand break via homologous recombination in vitro.
Dorsman et al. (2007) determined that the FANCI gene contains 38 exons, with translation starting in exon 2.
Crystal Structure
Joo et al. (2011) determined the crystal structure of the FANCI-FANCD2 (ID) complex at 3.4-angstrom resolution. The structure of the approximate 300-kD ID complex revealed that monoubiquitination and regulatory phosphorylation sites map to the I-D interface, suggesting that they occur on monomeric proteins or an opened-up complex and that they may serve to stabilize I-D heterodimerization. The 7.8-angstrom electron-density map of FANCI-DNA crystals and in vitro data showed that each protein has binding sites for both single- and double-stranded DNA, suggesting that the ID complex recognizes DNA structures that result from the encounter of replication forks with an interstrand crosslink.
Cryoelectron Microscopy
Using cryoelectron microscopy, Wang et al. (2020) determined the monoubiquitinated human ID complex bound to DNA, and revealed that it forms a closed ring that encircles the DNA. By comparison with the structure of the nonubiquitinated ID complex bound to interstrand crosslinked DNA, they showed that monoubiquitination triggers a complete rearrangement of the open, trough-like ID structure through the ubiquitin of one protomer binding to the other protomer in a reciprocal fashion. These structures, together with biochemical data, indicated that the monoubiquitinated ID complex loses its preference for interstrand crosslinks and related branched DNA structures, and becomes a sliding DNA clamp that can coordinate the subsequent repair reactions.
By genomic sequence analysis, Dorsman et al. (2007) mapped the FANCI gene to chromosome 15q25-q26.
Dorsman et al. (2007) identified several mutations in the FANCI gene (e.g., 611360.0001-611360.0004) in 8 patients with FA complementation group I (FANCI; 609053). Western blot analysis confirmed that functionally active FANCI protein was absent in patients with FA complementation group I. Sims et al. (2007) and Smogorzewska et al. (2007) also reported mutations in the FANCI gene in patients with FA complementation group I.
In a Turkish female with Fanconi anemia complementation group I (FANCI; 609053), Dorsman et al. (2007) identified a homozygous T-to-C transition at nucleotide 2 of the FANCI cDNA, resulting in removal of the translation initiation site. The patient had consanguineous parents and died at age 6.5 years. Sims et al. (2007) identified the same mutation and noted that it produces a new start codon at met94.
In 2 Indian sibs with Fanconi anemia complementation group I (FANCI; 609053), Dorsman et al. (2007) identified a homozygous G-to-A transition at nucleotide 3854 in exon 36 of the FANCI cDNA, resulting in an arg1285-to-gln (R1285Q) substitution. The mutation removed a highly conserved amino acid and created an additional ATM/ATR phosphorylation motif. The patients had consanguineous parents and died at ages 15 and 23 years. Both patients were also homozygous for a polymorphism, a C-to-T change at nucleotide 164 that resulted in a pro77-to-leu (P77L) substitution. This polymorphism was present in nearly 10% of healthy Dutch individuals. Smogorzewska et al. (2007) identified the same mutation and polymorphism in these patients and confirmed that R1285Q was the disease-causing mutation.
In a male Hungarian child with Fanconi anemia complementation group I (FANCI; 609053) who had nonconsanguineous parents, Dorsman et al. (2007) identified compound heterozygosity for mutations in the FANCI gene. The mutation on the maternal allele was a C-to-T transition at nucleotide 3853 in exon 37 of the FANCI cDNA, resulting in an arg1285-to-ter (R964X) substitution. The mutation on the paternal allele was an A-to-G transition at nucleotide -88 in intron 31 (3350-88A-G using the cDNA numbering; 611360.0004), which created a novel splice donor site and resulted in an additional exon. The patient died at age 12 years.
For discussion of the splice site mutation in the FANCI gene (3350-88A-G) that was found in compound heterozygous state in a patient with Fanconi anemia complementation group I (FANCI; 609053) by Dorsman et al. (2007), see 611360.0003.
Dorsman, J. C., Levitus, M., Rockx, D., Rooimans, M. A., Oostra, A. B., Haitjema, A., Bakker, S. T., Steltenpool, J., Schuler, D., Mohan, S., Schindler, D., Arwert, F., Pals, G., Mathew, C. G., Waisfisz, Q., de Winter, J. P., Joenje, H. Identification of the Fanconi anemia complementation group I gene, FANCI. Cell. Oncol. 29: 211-218, 2007. [PubMed: 17452773] [Full Text: https://doi.org/10.1155/2007/151968]
Joo, W., Xu, G., Persky, N. S., Smogorzewska, A., Rudge, D. G., Buzovetsky, O., Elledge, S. J., Pavletich, N. P. Structure of the FANCI-FANCD2 complex: insights into the Fanconi anemia DNA repair pathway. Science 333: 312-316, 2011. [PubMed: 21764741] [Full Text: https://doi.org/10.1126/science.1205805]
Knipscheer, P., Raschle, M., Smogorzewska, A., Enoiu, M., Ho, T. V., Scharer, O. D., Elledge, S. J., Walter, J. C. The Fanconi anemia pathway promotes replication-dependent DNA interstrand cross-link repair. Science 326: 1698-1701, 2009. [PubMed: 19965384] [Full Text: https://doi.org/10.1126/science.1182372]
Liu, T., Ghosal, G., Yuan, J., Chen, J., Huang, J. FAN1 acts with FANCI-FANCD2 to promote DNA interstrand cross-link repair. Science 329: 693-696, 2010. [PubMed: 20671156] [Full Text: https://doi.org/10.1126/science.1192656]
Long, D. T., Raschle, M., Joukov, V., Walter, J. C. Mechanism of RAD51-dependent DNA interstrand cross-link repair. Science 333: 84-87, 2011. [PubMed: 21719678] [Full Text: https://doi.org/10.1126/science.1204258]
Nagase, T., Nakayama, M., Nakajima, D., Kikuno, R., Ohara, O. Prediction of the coding sequences of unidentified human genes. XX. The complete sequences of 100 new cDNA clones from brain which code for large proteins in vitro. DNA Res. 8: 85-95, 2001. [PubMed: 11347906] [Full Text: https://doi.org/10.1093/dnares/8.2.85]
Sims, A. E., Spiteri, E., Sims, R. J., III, Arita, A. G., Lach, F. P., Landers, T., Wurm, M., Freund, M., Neveling, K., Hanenberg, H., Auerbach, A. D., Huang, T. T. FANCI is a second monoubiquitinated member of the Fanconi anemia pathway. Nature Struct. Molec. Biol. 14: 564-567, 2007. [PubMed: 17460694] [Full Text: https://doi.org/10.1038/nsmb1252]
Smogorzewska, A., Matsuoka, S., Vinciguerra, P., McDonald, E. R., III, Hurov, K. E., Luo, J., Ballif, B. A., Gygi, S. P., Hofmann, K., D'Andrea, A. D., Elledge, S. J. Identification of the FANCI protein, a monoubiquitinated FANCD2 paralog required for DNA repair. Cell 129: 289-301, 2007. [PubMed: 17412408] [Full Text: https://doi.org/10.1016/j.cell.2007.03.009]
Wang, R., Wang, S., Dhar, A., Peralta, C., Pavletich, N. P. DNA clamp function of the monoubiquitinated Fanconi anaemia ID complex. Nature 580: 278-282, 2020. [PubMed: 32269332] [Full Text: https://doi.org/10.1038/s41586-020-2110-6]