Alternative titles; symbols
HGNC Approved Gene Symbol: RAD23B
Cytogenetic location: 9q31.2 Genomic coordinates (GRCh38): 9:107,283,279-107,332,194 (from NCBI)
RAD23A (600061) and RAD23B, the human orthologs of yeast rad23, play distinct roles in nucleotide excision DNA repair (NER) and in the ubiquitin-proteasome system (UPS). NER is a genome maintenance pathway responsible for repair of bulky DNA lesions, and UPS performs protein degradation in diverse cellular processes, including DNA repair (summary by Bergink et al., 2013).
Masutani et al. (1994) cloned human RAD23A and RAD23B, which they called HHR23A and HHR23B, from a HeLa cell cDNA library. The deduced proteins contain 363 and 409 amino acids, respectively, and both have an N-terminal domain that shares significant similarity with ubiquitin (UBB; 191339) and various ubiquitin fusion proteins. Both RAD23A and RAD23B were expressed in the same cells.
In mouse, van der Spek et al. (1996) cloned the homologs of both RAD23A and RAD23B. Detailed sequence comparisons permitted deductions concerning the structure of all RAD23 homologs. Northern blot analysis revealed constitutive expression of both RAD23 genes in all tissues examined. Elevated RNA expression of both genes was observed in testis.
Using a DNA damage recognition-competition assay, Sugasawa et al. (1998) identified XPC-RAD23B as the earliest damage detector to initiate NER; it acts before the known damage-binding protein XPA. Coimmunoprecipitation and DNase I footprinting showed that XPC-RAD23B binds to a variety of NER lesions. This provides a plausible explanation for the extreme damage specificity exhibited by global genome repair.
Machado-Joseph disease (MJD; 109150) is an autosomal dominant neurodegenerative disorder caused by an expansion of the polyglutamine tract near the C terminus of the MJD1 gene product, ataxin-3. The mutant ataxin-3 forms intranuclear inclusions in cultured cells as well as in diseased human brain and also causes cell death in transfected cells. Using a 2-hybrid system, Wang et al. (2000) found that ataxin-3 interacts with 2 human homologs of the yeast DNA repair protein RAD23, RAD23A and RAD23B. Both normal and mutant ataxin-3 proteins interact with the ubiquitin-like domain at the N terminus of the HHR23 proteins, which is a motif important for nucleotide excision repair. However, in human embryonic kidney cells, HHR23A is recruited to intranuclear inclusions formed by the mutant ataxin-3 through its interaction with ataxin-3. The authors suggested that this interaction is associated with the normal function of ataxin-3, and that some functional abnormality of the RAD23 proteins may exist in MJD.
Volker et al. (2001) described the assembly of the NER complex in normal and repair-deficient (xeroderma pigmentosum) human cells by employing a novel technique of local ultraviolet irradiation combined with fluorescent antibody labeling. The damage-recognition complex XPC (613208)-HHR23B appeared to be essential for the recruitment of all subsequent NER factors in the preincision complex, including transcription repair factor TFIIH (see 189972). Volker et al. (2001) found that XPA (611153) associates relatively late, is required for anchoring of ERCC1 (126380)-XPF (133520), and may be essential for activation of the endonuclease activity of XPG (133530). These findings identified XPC as the earliest known NER factor in the reaction mechanism, gave insight into the order of subsequent NER components, provided evidence for a dual role of XPA, and supported a concept of sequential assembly of repair proteins at the site of damage rather than a preassembled repairosome. The XPC-RAD23B complex is specifically involved in global genome but not transcription-coupled NER.
Chen and Madura (2006) stated that HHR23A and HHR23B have redundant roles in DNA repair. However, they presented evidence that the 2 proteins have distinct functions in protein degradation. Full-length RAD23B and its isolated UBB-like domain bound yeast and human proteasome subunits with higher affinity than RAD23A. RAD23B was also associated with higher proteasome-dependent chymotryptic activity than RAD23A. Protein pull-down, mass spectrometry, and Western blot analyses revealed that the 2 proteins bound overlapping but distinct sets of multiubiquitinated proteins, proteasome subunits, stress response proteins, and elongation factors. Mutation analysis revealed that thr79 in RAD23A inhibited proteasome binding, and substitution of thr79 with pro, which is found in RAD23B, increased the ability of RAD23A to bind proteasome subunits. The substitution had no effect on the binding of RAD23A to multiubiquitinated proteins. Mutation analysis further revealed that lys8 of RAD23A and lys6 of RAD23B were critical for binding to proteasome subunits, but not to ataxin-3 (ATXN3; 607047). Chen and Madura (2006) concluded that RAD23A and RAD23B are likely to perform distinct cellular functions that require the proteasome.
Yasuda et al. (2020) demonstrated that proteasome-containing nuclear foci form under acute hyperosmotic stress. These foci are transient structures that contain ubiquitylated proteins, valosin-containing protein (VCP; 601023), and multiple proteasome-interacting proteins, which collectively constitute a proteolytic center. The major substrates for degradation by these foci were ribosomal proteins that failed to properly assemble. Notably, the proteasome foci exhibited properties of liquid droplets. RAD23B, a substrate-shuttling factor for the proteasome, and ubiquitylated proteins were necessary for formation of proteasome foci. In mechanistic terms, a liquid-liquid phase separation was triggered by multivalent interactions of 2 ubiquitin-associated domains of RAD23B and ubiquitin chains consisting of 4 or more ubiquitin molecules. Yasuda et al. (2020) concluded that their results suggested that ubiquitin chain-dependent phase separation induces the formation of a nuclear proteolytic compartment that promotes proteasomal degradation.
Van der Spek et al. (1994) reported that the RAD23B and XPC genes, the products of which form a tight complex, colocalize on chromosome 3p25.1. However, Gross (2014) mapped the RAD23B gene to chromosome 9q31.2 based on an alignment of the RAD23B sequence (GenBank BC020973) with the genomic sequence (GRCh37).
Van der Spek et al. (1996) found that the mouse Xpc and Rad23b genes are on different chromosomes, namely 6B and 4B3, respectively.
Ng et al. (2002) created a Rad23b knockout mouse model. Fibroblasts cultured from embryonic animals were not UV sensitive and retained the repair characteristics of wildtype cells, suggesting that Rad23a can functionally replace Rad23b in NER. However, there was a high rate of intrauterine or neonatal death in Rad23b -/- animals, and surviving animals displayed a variety of abnormalities, including retarded growth, facial dysmorphology, and male sterility. These findings suggested a function for Rad23b in normal development that cannot be compensated for by Rad23a.
Bergink et al. (2013) obtained Rad23b -/- mice in less than the expected mendelian ratio. At midgestation, Rad23b -/- embryos were anemic, although surviving Rad23b -/- adults were not. Rad23b -/- embryos showed normal primitive erythropoiesis in the yolk sac, but they exhibited impaired transition to definitive erythropoiesis in fetal liver around embryonic day 11. Mass spectrometry indicated that most of Rad23b-interacting proteins were cell cycle regulators and proteins of the UPS. Rad23b -/- mouse embryonic fibroblasts and fetal liver erythroid cells showed a defect in proliferation, with a delay in G2/M transition. Inhibition of the proteasome resulted in a similar phenotype in wildtype erythroid cells. Bergink et al. (2013) concluded that RAD23B is critical for proteasome-dependent erythropoiesis.
Bergink, S., Theil, A. F., Toussaint, W., De Cuyper, I. M., Kulu, D. I., Clapes, T., van der Linden, R., Demmers, J. A., Mul, E. P., van Alphen, F. P., Marteijn, J. A., van Gent, T., Maas, A., Robin, C., Philipsen, S., Vermeulen, W., Mitchell, J. R., Gutierrez, L. Erythropoietic defect associated with reduced cell proliferation in mice lacking the 26S proteasome shuttling factor Rad23b. Molec. Cell. Biol. 33: 3879-3892, 2013. [PubMed: 23897431] [Full Text: https://doi.org/10.1128/MCB.05772-11]
Chen, L., Madura, K. Evidence for distinct functions for human DNA repair factors hHR23A and hHR23B. FEBS Lett. 580: 3401-3408, 2006. [PubMed: 16712842] [Full Text: https://doi.org/10.1016/j.febslet.2006.05.012]
Gross, M. B. Personal Communication. Baltimore, Md. 6/2/2014.
Masutani, C., Sugasawa, K., Yanagisawa, J., Sonoyama, T., Ui, M., Enomoto, T., Takio, K., Tanaka, K., van der Spek, P. J., Bootsma, D., Hoeijmakers, J. H. J., Hanaoka, F. Purification and cloning of a nucleotide excision repair complex involving the xeroderma pigmentosum group C protein and a human homologue of yeast RAD23. EMBO J. 13: 1831-1843, 1994. [PubMed: 8168482] [Full Text: https://doi.org/10.1002/j.1460-2075.1994.tb06452.x]
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van der Spek, P. J., Smit, E. M. E., Beverloo, H. B., Sugasawa, K., Masutani, C., Hanaoka, F., Hoeijmakers, J. H. J., Hagemeijer, A. Chromosomal localization of three repair genes: the xeroderma pigmentosum group C gene and two human homologs of yeast RAD23. Genomics 23: 651-658, 1994. [PubMed: 7851894] [Full Text: https://doi.org/10.1006/geno.1994.1554]
van der Spek, P. J., Visser, C. E., Hanaoka, F., Smit, B., Hagemeijer, A., Bootsma, D., Hoeijmakers, J. H. J. Cloning, comparative mapping, and RNA expression of the mouse homologues of the Saccharomyces cerevisiae nucleotide excision repair gene RAD23. Genomics 31: 20-27, 1996. [PubMed: 8808275] [Full Text: https://doi.org/10.1006/geno.1996.0004]
Volker, M., Mone, M. J., Karmakar, P., van Hoffen, A., Schul, W., Vermeulen, W., Hoeijmakers, J. H. J., van Driel, R., van Zeeland, A. A., Mullenders, L. H. F. Sequential assembly of the nucleotide excision repair factors in vivo. Molec. Cell 8: 213-224, 2001. [PubMed: 11511374] [Full Text: https://doi.org/10.1016/s1097-2765(01)00281-7]
Wang, G., Sawai, N., Kotliarova, S., Kanazawa, I., Nukina, N. Ataxin-3, the MJD1 gene product, interacts with the two human homologs of yeast DNA repair protein RAD23, HHR23A and HHR23B. Hum. Molec. Genet. 9: 1795-1803, 2000. [PubMed: 10915768] [Full Text: https://doi.org/10.1093/hmg/9.12.1795]
Yasuda, S., Tsuchiya, H., Kaiho, A., Guo, Q., Ikeuchi, K., Endo, A., Arai, N., Ohtake, F., Murata, S., Inada, T., Baumeister, W., Fernandez-Busnadiego, R., Tanaka, K., Saeki, Y. Stress- and ubiquitylation-dependent phase separation of the proteasome. Nature 578: 296-300, 2020. [PubMed: 32025036] [Full Text: https://doi.org/10.1038/s41586-020-1982-9]