Fanconi anemia group B protein is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

that in humans is encoded by the ''FANCB''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

Function

The Fanconi anemia complementation group (FANC) currently includes

FANCA 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 ...

, FANCB,

FANCC Fanconi anemia group C protein is a protein that in humans is encoded by the ''FANCC'' gene. Structure Function The protein encoded by this gene delays the onset of apoptosis and promotes homologous recombination repair of damaged DNA. M ...

FANCD1 ''BRCA2'' and BRCA2 () are a human gene and its protein product, respectively. The official symbol (BRCA2, italic for the gene, nonitalic for the protein) and the official name (originally breast cancer 2; currently BRCA2, DNA repair associated) ...

(also called BRCA2),

FANCD2 Fanconi anemia group D2 protein is a protein that in humans is encoded by the ''FANCD2'' gene. The Fanconi anemia complementation group ( FANC) currently includes FANCA, FANCB, FANCC, FANCD1 (also called BRCA2), FANCD2 (this gene), FANCE, FANCF, FA ...

FANCE Fanconi anemia, complementation group E protein is a protein that in humans is encoded by the ''FANCE'' gene. The Fanconi anemia complementation group (FANC) currently includes FANCA, FANCB, FANCC, FANCD1 (also called BRCA2), FANCD2, FANCE, FANC ...

FANCF Fanconi anemia group F protein is a protein that in humans is encoded by the ''FANCF'' gene. Interactions FANCF has been shown to interact with Fanconi anemia, complementation group C, FANCG, FANCA and FANCE. Function FANCF is an adaptor pro ...

FANCG Fanconi anemia group G protein is a protein that in humans is encoded by the ''FANCG'' gene. Function FANCG, involved in Fanconi anemia, confers resistance to both hygromycin B and mitomycin C. FANCG contains a 5-prime GC-rich untranslated r ...

, and

FANCL E3 ubiquitin-protein ligase FANCL is an enzyme that in humans is encoded by the ''FANCL'' gene. Function The clinical phenotype of mutational defects in all Fanconi anemia (FA) complementation groups is similar. This phenotype is characteriz ...

Fanconi anemia Fanconi anaemia (FA) is a rare genetic disease resulting in impaired response to DNA damage. Although it is a very rare disorder, study of this and other bone marrow failure syndromes has improved scientific understanding of the mechanisms of no ...

is a genetically heterogeneous recessive disorder characterized by cytogenetic instability, hypersensitivity to DNA crosslinking agents, increased chromosomal breakage, and defective

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

. The members of the Fanconi anemia complementation group do not share sequence similarity; they are related by their assembly into a common nuclear protein complex. This gene encodes the protein for complementation group B. Alternative splicing results in two transcript variants encoding the same protein.

Gene

FANCB is the only gene known to cause

X-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, ...

Fanconi Anemia. In female carriers of FANCB mutations (one wild-type FANCB allele and one mutant FANCB allele) there is strong selection through

X-inactivation X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into ...

for expression of only the wild-type allele. In contrast, males have only one FANCB allele. Only male patients with Fanconi anemia have ever been linked to FANCB mutations, and they make up about 4% of cases. Mutation in the FANCB are highly associated with the development of the VACTERL-H constilation of birth defects. In a cohort study of 19 children with FANCB variants, those with deletion of FANCB gene or truncation of FANCB protein demonstrate earlier-than-average onset of bone marrow failure and more severe congenital abnormalities compared with a large series of Fanconi Anemia individuals in published reports. This reflects the indispensable role of FANCB gene in cells. For FANCB missense variants, more variable severity is associated with the extent of residual activity.

Protein

The FANCB gene product is FANCB protein. FANCB is a component of a "core complex" of nine Fanconi Anemia proteins:

, FANCB,

, FAAP100 and FAAP20. The core complex localises to DNA damage sites during

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

where it catalyzes transfer of

ubiquitin Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...

and

FANCI Fanconi anemia, complementation group I (FANCI) also known as KIAA1794, is a protein which in humans is encoded by the ''FANCI'' gene. Mutations in the ''FANCI'' gene are known to cause Fanconi anemia. Function The Fanconi anemia complementa ...

. In particular, this reaction is necessary for the repair of DNA interstrand crosslinks, such as those formed by chemotherapy drugs

cisplatin Cisplatin is a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, cervical cancer, breast cancer, bladder cancer, head and neck cancer, esophageal cancer, lung cancer, mesothelioma, br ...

mitomycin c Mitomycin C is a mitomycin that is used as a chemotherapeutic agent by virtue of its antitumour activity. Medical uses It is given intravenously to treat upper gastro-intestinal cancers (e.g. esophageal carcinoma), anal cancers, and breast c ...

and

melphalan Melphalan, sold under the brand name Alkeran among others, is a chemotherapy medication used to treat multiple myeloma, ovarian cancer, melanoma, and AL amyloidosis. It is taken by mouth or by injection into a vein. Common side effects incl ...

. Within the Fanconi anemia core complex, FANCB has an obligate interaction with FAAP100 and FANCL, to form a catalytic E3 RING ligase enzyme. FANCB creates a dimer interface within this subcomplex that is required for simultaneous ubiquitination of FANCD2 and FANCI. Electron microscopy imaging of the FANCB-FANCL-FAAP100 complex revealed a symmetry that is centred on FANCB, and biochemical investigation confirmed that the entire complex is a dimer containing two of each subunit. Further imaging reveals the overall architecture of the Fanconi Anemia core complex centres on FANCB protein.

Meiosis

FANCB mutant mice are

infertile Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...

and exhibit primordial

germ cell Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embry ...

defects during

embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

. The germ cells and

testicular A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosteron ...

size are severely compromised in FANCB mutant mice. FANCB protein is essential for

spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubule ...

and likely has a role in the activation of the Fanconi anemia DNA repair pathway during

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

References

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