Alternative titles; symbols
HGNC Approved Gene Symbol: UBE2B
Cytogenetic location: 5q31.1 Genomic coordinates (GRCh38): 5:134,371,569-134,392,108 (from NCBI)
As deduced from the pleiotropic phenotype of rad6 deletion mutants in Saccharomyces cerevisiae, the RAD6 protein plays an important role in various cellular processes. The protein is strongly conserved in eukaryotic evolution, a property that permitted Koken et al. (1991) to clone 2 human homologs by evolutionary walking using Schizosaccharomyces pombe and Drosophila melanogaster homologs as 'intermediates.' The human HHR6A (UBE2A; 312180) and HHR6B proteins (HHR for human homolog of rad6) shared about 95% amino acid sequence identity with each other and about 70% amino acid sequence with their yeast counterparts, but notably lacked the acidic C-terminal domain, the occurrence of which seemed to be limited to S. cerevisiae rad6.
By in situ hybridization using a biotinylated probe, Koken et al. (1992) assigned the UBE2B gene, the human homolog of yeast rad6, to chromosome 5q23-q31. Studies in interspecific backcrosses by Roller et al. (1995) showed 2 genes related to UBE2B in the mouse: one mapped to mouse chromosome 13, which shows homology to human 5q and may represent the functional gene. A second maps to a region of chromosome 11 with homology to human chromosome 17 and may represent a pseudogene.
Lench et al. (1995) used PCR to detect polymorphisms in a (CGG)n trinucleotide repeat sequence in the 5-prime region of the UBE2B DNA repair gene.
The RAD6 pathway is central to postreplicative DNA repair in eukaryotic cells. Two principal elements of this pathway are the ubiquitin-conjugating enzymes RAD6 and the MMS2 (603001)-UBC13 (603679) heterodimer, which are recruited to chromatin by the RING-finger proteins RAD18 (605256) and RAD5 (608048), respectively. Hoege et al. (2002) showed that UBC9 (601661), a small ubiquitin-related modifier (SUMO)-conjugating enzyme, is also affiliated with this pathway and that proliferating cell nuclear antigen (PCNA; 176740), a DNA polymerase sliding clamp involved in DNA synthesis and repair, is a substrate. PCNA is monoubiquitinated through RAD6 and RAD18, modified by lys63-linked multiubiquitination, which additionally requires MMS2, UBC13, and RAD5, and is conjugated to SUMO by UBC9. All 3 modifications affect the same lysine residue of PCNA, K164, suggesting that they label PCNA for alternative functions. Hoege et al. (2002) demonstrated that these modifications differentially affect resistance to DNA damage, and that damage-induced PCNA ubiquitination is elementary for DNA repair and occurs at the same conserved residue in yeast and humans.
Ulrich and Jentsch (2000) demonstrated that RAD18 and RAD5 play a central role in mediating physical contacts between the members of the RAD6 pathway. RAD5 recruits the UBC13-MMS2 complex to DNA by means of its RING finger domain. Moreover, RAD5 association with RAD18 brings UBC13-MMS2 into contact with the RAD6-RAD18 complex. Interaction between the 2 RING finger proteins thus promotes the formation of a heteromeric complex in which the 2 distinct ubiquitin-conjugating activities of RAD6 and UBC13-MMS2 can be closely coordinated. Ulrich and Jentsch (2000) found that while UBC13 and MMS2 are largely cytosolic proteins, DNA damage triggers their redistribution to the nucleus.
Hishida et al. (2009) examined the response of yeast cells to chronic low dose ultraviolet light (CLUV) and identified a key role for the RAD6-RAD18 (605256)-RAD5 (608048) error-free postreplication repair (PRR) pathway in promoting cell growth and survival. They found that loss of the RAD6 error-free PRR pathway resulted in DNA damage checkpoint-induced G2 arrest in CLUV-exposed cells, whereas wildtype and nucleotide excision repair-deficient cells were largely unaffected. Cell cycle arrest in the absence of the RAD6 error-free PRR pathway was not caused by a repair defect or by the accumulation of ultraviolet-induced photoproducts. Hishida et al. (2009) observed increased replication protein A (RPA; see 179835)- and Rad52 (600392)-yellow fluorescent protein foci in the CLUV-exposed Rad18 (605256)-delta cells and demonstrated that Rad52-mediated homologous recombination is required for the viability of the Rad18-delta cells after release from CLUV-induced G2 arrest. These and other data presented suggested that, in response to environmental levels of ultraviolet exposure, the RAD6 error-free PRR pathway promotes replication of damaged templates without the generation of extensive single-stranded DNA regions. Thus this pathway is specifically important during chronic low-dose ultraviolet exposure to prevent counterproductive DNA checkpoint activation and allow cells to proliferate normally.
Roest et al. (1996) reported the phenotype of the first animal mutant in the ubiquitin pathway. Experimental inactivation of the RAD6B gene in mice caused male infertility. Derailment of spermatogenesis became overt during the postmeiotic condensation of chromatin in spermatids. In yeast the gene is not only implicated in postreplication repair and damage-induced mutagenesis but is also required for sporulation and may modulate chromatin structure via histone ubiquitination. The authors stated that the findings in the 'knock-out' mice provided a parallel between yeast sporulation and mammalian spermatogenesis and strongly implicated RAD6-dependent ubiquitination in chromatin remodeling in the human. Since heterozygous male mice and even knockout female mice are completely normal and fertile and thus able to transmit the defect, similar RAD6B mutations may cause male infertility in man. The fact that the RAD6B mice are viable and phenotypically normal is presumably due to functional redundancy with RAD6A (312180).
Baarends et al. (2003) determined that primary spermatocytes of Hr6b knockout mice underwent increased apoptosis during meiotic prophase. In the absence of Hr6b, the structure and telomere localization of synaptonemal complexes were altered within the nuclei of pachytene and diplotene spermatocytes. The number of foci containing the mismatch DNA repair protein Mlh1 (120436) was increased and reflected a consistent 20 to 25% increase in crossing-over frequency in mutant spermatocytes. Baarends et al. (2003) concluded that the ubiquitin-conjugating activity of HR6B is required within the synaptonemal complex and for meiotic recombination in spermatocytes.
Baarends, W. M., Wassenaar, E., Hoogerbrugge, J. W., van Cappellen, G., Roest, H. P., Vreeburg, J., Ooms, M., Hoeijmakers, J. H. J., Grootegoed, J. A. Loss of HR6B ubiquitin-conjugating activity results in damaged synaptonemal complex structure and increased crossing-over frequency during the male meiotic prophase. Molec. Cell. Biol. 23: 1151-1162, 2003. [PubMed: 12556476] [Full Text: https://doi.org/10.1128/MCB.23.4.1151-1162.2003]
Hishida, T., Kubota, Y., Carr, A. M., Iwasaki, H. RAD6-RAD18-RAD5-pathway-dependent tolerance to chronic low-dose ultraviolet light. Nature 457: 612-615, 2009. [PubMed: 19079240] [Full Text: https://doi.org/10.1038/nature07580]
Hoege, C., Pfander, B., Moldovan, G.-L., Pyrowolakis, G., Jentsch, S. RAD6-dependent DNA repair is linked to modification of PCNA by ubiquitin and SUMO. Nature 419: 135-141, 2002. [PubMed: 12226657] [Full Text: https://doi.org/10.1038/nature00991]
Koken, M. H. M., Reynolds, P., Jaspers-Dekker, I., Prakash, L., Prakash, S., Bootsma, D., Hoeijmakers, J. H. J. Structural and functional conservation of two human homologs of the yeast DNA repair gene RAD6. Proc. Nat. Acad. Sci. 88: 8865-8869, 1991. [PubMed: 1717990] [Full Text: https://doi.org/10.1073/pnas.88.20.8865]
Koken, M. H. M., Smit, E. M. E., Jaspers-Dekker, I., Oostra, B. A., Hagemeijer, A., Bootsma, D., Hoeijmakers, J. H. J. Localization of two human homologs, HHR6A and HHR6B, of the yeast DNA repair gene RAD6 to chromosomes Xq24-q25 and 5q23-q31. Genomics 12: 447-453, 1992. [PubMed: 1559696] [Full Text: https://doi.org/10.1016/0888-7543(92)90433-s]
Lench, N. J., Thompson, J., Markham, A. F., Robinson, P. A. (CGG) trinucleotide repeat polymorphism in the 5-prime region of the HHR6B gene: the human homolog of the yeast DNA repair gene RAD6. Hum. Genet. 96: 369-370, 1995. [PubMed: 7649561] [Full Text: https://doi.org/10.1007/BF00210428]
Roest, H. P., van Klaveren, J., de Wit, J., van Gurp, C. G., Koken, M. H. M., Vermey, M., van Roijen, J. H., Hoogerbrugge, J. W., Vreeburg, J. T. M., Baarends, W. M., Bootsma, D., Grootegoed, J. A., Hoeijmakers, J. H. J. Inactivation of the HR6B ubiquitin-conjugating DNA repair enzyme in mice causes male sterility associated with chromatin modification. Cell 86: 799-810, 1996. [PubMed: 8797826] [Full Text: https://doi.org/10.1016/s0092-8674(00)80154-3]
Roller, M. L., Lossie, A. C., Koken, M. H. M., Smit, E. M. E., Hagemeijer, A., Camper, S. A. Localization of sequences related to the human RAD6 DNA repair gene on mouse chromosomes 11 and 13. Mammalian Genome 6: 305-306, 1995. [PubMed: 7613042] [Full Text: https://doi.org/10.1007/BF00352425]
Ulrich, H. D., Jentsch, S. Two RING finger proteins mediate cooperation between ubiquitin-conjugating enzymes in DNA repair. EMBO J. 19: 3388-3397, 2000. [PubMed: 10880451] [Full Text: https://doi.org/10.1093/emboj/19.13.3388]