FANCA

217514087ENSG00000187741ENSMUSG00000032815O15360Q9JL70NM_000135NM_001018112NM_001286167NM_001351830NM_016925NP_000126NP_001018122NP_001273096NP_001338759NP_058621Fanconi anaemia, complementation group A, also known as FAA, FACA and FANCA, is a protein which in humans is encoded by the FANCA gene. It belongs to the Fanconi anaemia complementation group (FANC) family of genes of which 12 complementation groups are currently recognized and is hypothesised to operate as a post-replication repair or a cell cycle checkpoint. FANCA proteins are involved in inter-strand DNA cross-link repair and in the maintenance of normal chromosome stability that regulates the differentiation of haematopoietic stem cells into mature blood cells. Fanconi anaemia, complementation group A, also known as FAA, FACA and FANCA, is a protein which in humans is encoded by the FANCA gene. It belongs to the Fanconi anaemia complementation group (FANC) family of genes of which 12 complementation groups are currently recognized and is hypothesised to operate as a post-replication repair or a cell cycle checkpoint. FANCA proteins are involved in inter-strand DNA cross-link repair and in the maintenance of normal chromosome stability that regulates the differentiation of haematopoietic stem cells into mature blood cells. Mutations involving the FANCA gene are associated with many somatic and congenital defects, primarily involving phenotypic variations of Fanconi anaemia, aplastic anaemia, and forms of cancer such as squamous cell carcinoma and acute myeloid leukaemia. The Fanconi anaemia complementation group (FANC) currently includes FANCA, FANCB, FANCC, FANCD1 (also called BRCA2), FANCD2, FANCE, FANCF, FANCG, and FANCL. The previously defined group FANCH is the same as FANCA. The members of the Fanconi anaemia complementation group do not share sequence similarity; they are related by their assembly into a common nuclear protein complex. The FANCA gene encodes the protein for complementation group A. Alternative splicing results in multiple transcript variants encoding different isoforms. In humans, the gene FANCA is 79 kilobases (kb) in length, and is located on chromosome 16 (16q24.3). The FANCA protein is composed of 1455 amino acids. Within cells, the major purpose of FANCA belongs to its putative involvement in a multisubunit FA complex composed of FANCA, FANCB, FANCC, FANCE, FANCF, FANCG, FANCL/PHF9 and FANCM. In complex with FANCF, FANCG and FANCL, FANCA interacts with HES1. This interaction has been proposed as essential for the stability and nuclear localization of FA core complex proteins. The complex with FANCC and FANCG may also include EIF2AK2 and HSP70. In cells, FANCA involvement in this ‘FA core complex’ is required for the activation of the FANCD2 protein to a monoubiquitinated isoform (FANCD2-Ub) in response to DNA damage, catalysing activation of the FA/BRCA DNA damage-response pathway, leading to repair. FANCA binds to both single-stranded (ssDNA) and double-stranded (dsDNA) DNAs; however, when tested in an electrophoretic mobility shift assay, its affinity for ssDNA is significantly higher than for dsDNA. FANCA also binds to RNA with a higher affinity than its DNA counterpart. FANCA requires a certain number of nucleotides for optimal binding, with the minimum for FANCA recognition being approximately 30 for both DNA and RNA. Yuan et al. (2012) found through affinity testing FANCA with a variety of DNA structures that a 5'-flap or 5'-tail on DNA facilitates its interaction with FANCA, while the complementing C-terminal fragment of Q772X, C772-1455, retains the differentiated nucleic acid-binding activity (i.e. preferencing RNA before ssDNA and dsDNA), indicating that the nucleic acid-binding domain of FANCA is located primarily at the C terminus, a location where many disease-causing mutations are found. FANCA is ubiquitously expressed at low levels in all cells with subcellular localisation in primarily nucleus but also cytoplasm corresponding with its putative caretaker role in DNA damage-response pathways, and FA complex formation. The distribution of proteins in different tissues is not well understood currently. Immunochemical study of mouse tissue indicates that FANCA is present at a higher level in lymphoid tissues, the testis and the ovary, and though the significance of this is unclear, it suggests that the presence of FA proteins might be related to cellular proliferation. For example, in human immortalized lymphoblasts and leukaemia cells, FA proteins are readily detectable by immunoprecipitation. Mutations in this gene are the most common cause of Fanconi's anaemia. Fanconi anaemia is an inherited autosomal recessive disorder, the main features of which are aplastic anaemia in childhood, multiple congenital abnormalities, susceptibility to leukemia and other cancers, and cellular hypersensitivity to interstrand DNA cross-linking agents. Generally cells from Fanconi anaemia patients show a markedly higher frequency of spontaneous chromosomal breakage and hypersensitivity to the clastogenic effect of DNA cross-linking agents such as diepoxybutane (DEB) and mitomycin-C (MMC) when compared to normal cells. The primary diagnostic test for Fanconi anaemia is based on the increased chromosomal breakage seen in afflicted cells after exposure to these agents – the DEB/MMC stress test. Other features of the Fanconi anaemia cell phenotype also include abnormal cell cycle kinetics (prolonged G2 phase), hypersensitivity to oxygen, increased apoptosis and accelerated telomere shortening. FANCA mutations are by far the most common cause of Fanconi anaemia, accounting for between 60-70% of all cases. FANCA was cloned in 1996 and it is one of the largest FA genes. Hundreds of different mutations have been recorded with 30% point mutations, 30% 1-5 base pair microdeletions or microinsertions, and 40% large deletions, removing up to 31 exons from the gene. These large deletions have a high correlation with specific breakpoints and arise as a result of Alu mediated recombination. A highly relevant observation is that different mutations produce Fanconi anaemia phenotypes of varying severity. Patients homozygous for null-mutations in this gene have an earlier onset of anaemia than those with mutations that produce an altered or incorrect protein. However, as most patients are compound heterozygotes, diagnostic screening for mutations is difficult. Certain founder mutations can also occur in some populations, such as the deletion exon 12-31 mutation, which accounts for 60% of mutations in Afrikaners.