Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.30.2 (endonuclease)
18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

XPG is the human endonuclease that cuts 3' to DNA lesions during nucleotide excision repair. Missense mutations in XPG can lead to xeroderma pigmentosum (XP), whereas truncated or unstable XPG proteins cause Cockayne syndrome (CS), normally yielding life spans of <7 years. One XP-G individual who had advanced XP/CS symptoms at 28 years has been identified. The genetic, biochemical, and cellular defects in this remarkable case provide insight into the onset of XP and CS, and they reveal a previously unrecognized property of XPG. Both of this individual's XPG alleles produce a severely truncated protein, but an infrequent alternative splice generates an XPG protein lacking seven internal amino acids, which can account for his very slight cellular UV resistance. Deletion of XPG amino acids 225 to 231 does not abolish structure-specific endonuclease activity. Instead, this region is essential for interaction with TFIIH and for the stable recruitment of XPG to sites of local UV damage after the prior recruitment of TFIIH. These results define a new functional domain of XPG, and they demonstrate that recruitment of DNA repair proteins to sites of damage does not necessarily lead to productive repair reactions. This observation has potential implications that extend beyond nucleotide excision repair.
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PMID:Definition of a short region of XPG necessary for TFIIH interaction and stable recruitment to sites of UV damage. 1557 72

A novel endo-exonuclease, DmGEN (Drosophila Melanogaster XPG-like endonuclease), was identified in D.melanogaster. DmGEN is composed of five exons and four introns, and the open reading frame encodes a predicted product of 726 amino acid residues with a molecular weight of 82.5 kDa and a pI of 5.36. The gene locus on Drosophila polytene chromosomes was detected at 64C9 on the left arm of chromosome 3 as a single site. The encoded protein showed a relatively high degree of sequence homology with the RAD2 nucleases, especially XPG. Although the XPG-N- and XPG-I-domains are highly conserved in sequence, locations of the domains are similar to those of FEN-1 and EXO-1, and the molecular weight of the protein is close to that of EXO-1. In vitro, DmGEN showed endonuclease and 3'-5' exonuclease activities with both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), but the endonuclease action with dsDNA was quite specific: 5'-3' exonuclease activity was found to occur with nicked DNA, while dsDNA was endonucleolytically cut at 3-4 bp from the 5' end. Homologs are widely found in mammals and higher plants. The data suggest that DmGEN belongs to a new class of RAD2 nuclease.
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PMID:DmGEN, a novel RAD2 family endo-exonuclease from Drosophila melanogaster. 1557 51

XPG has structural and catalytic roles in nucleotide excision repair (NER) and belongs to the FEN-1 family of structure-specific nucleases. XPG contains a stretch of over 600 amino acids termed the "spacer region" between the conserved N- and I-nuclease regions. Its role is unknown, and it is not similar to any known protein. To investigate its possible functions, we generated and analyzed several deletion mutants of XPG. The spacer region is not required for endonuclease activity, but amino acids 111-550 contribute to the substrate specificity of XPG, and they are required for interaction with TFIIH and for NER activity in vitro and in vivo. Deletion of residues 184-210 and 554-730 leads only to a partial defect in NER activity and a weakened interaction with TFIIH. XPGDelta184-210 and XPGDelta554-730 are not observed at sites of local UV damage in living cells by immunofluorescence, suggesting that the weakened interaction between XPG and TFIIH results in an NER reaction with altered kinetics. This study demonstrates that the N-terminal portion of the spacer region is particularly important for NER progression by mediating the XPG-TFIIH interaction and XPG substrate specificity.
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PMID:The spacer region of XPG mediates recruitment to nucleotide excision repair complexes and determines substrate specificity. 1559 Jun 80

We have cloned a new member of the RAD2/XPG nuclease family, OsGEN-L (OsGEN-like), from rice (Oryza sativa L.). OsGEN-L possesses two domains, the N- and I-regions, that are conserved in the RAD2/XPG nuclease family. Database searches and phylogenetic analyses revealed that OsGEN-L belongs to class 4 of the RAD2/XPG nuclease family, and OsGEN-L homologs were found in animals and higher plants. To elucidate the function of OsGEN-L, we generated rice OsGEN-L-RNAi transgenic plants in which OsGEN-L expression was silenced. Most of the OsGEN-L-RNAi plants displayed low fertility, and some of them were male-sterile. OsGEN-L-RNAi plants lacked mature pollen, resulting from a defect in early microspore development. A OsGEN-L-green fluorescent protein (GFP) fusion protein was localized in the nucleus, and the OsGEN-L promoter was specifically active in the anthers. Furthermore, a recombinant OsGEN-L protein possessed flap endonuclease activity and both single-stranded and double-stranded DNA-binding activities. Our results suggest that OsGEN-L plays an essential role in DNA metabolism required for early microspore development in rice.
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PMID:RNAi-mediated silencing of OsGEN-L (OsGEN-like), a new member of the RAD2/XPG nuclease family, causes male sterility by defect of microspore development in rice. 1579 60

The severe xeroderma pigmentosum/Cockayne syndrome (XP/CS) syndrome is caused by mutations in the XPB, XPD and XPG genes that encode the helicase subunits of TFIIH and the 3' endonuclease of nucleotide excision repair (NER). Because XPB and XPD have been implicated in p53-mediated apoptosis, we examined the possible involvement of XPG in this process. After ultraviolet light (UV) irradiation, primary fibroblasts of XP complementation group G (XP-G) individuals with CS enter apoptosis more readily than other NER-deficient cells, but this is unlinked to unrepaired damage. These XP-G/CS cells accumulate p53 post-UV but they fail to accumulate the 90/92 kDa isoforms of Mdm2 and their cellular distribution of Mdm2 is impaired. Apoptosis levels revert to wild type, Mdm2 90/92 kDa isoforms accumulate, and Mdm2 regains its normal post-UV nuclear location in transduced XP-G/CS cells expressing wild-type XPG, but not an XPG catalytic site mutant. These results suggest that XPG suppresses UV-induced apoptosis and that this suppression, most simply, requires its endonuclease function.
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PMID:Suppression of UV-induced apoptosis by the human DNA repair protein XPG. 1616 68

There are more than 50 subtypes of soft tissue sarcomas, among which 30% are associated with specific genetic alterations, including translocations. Several studies have reported associations between cancer risk and polymorphisms of DNA repair genes from the nucleotide excision repair (NER) pathway. NER involves more than 20 proteins whose inactivation leads to xeroderma pigmentosum (XP) or cockayne syndrome (CS), among which XPD, a helicase allowing DNA strand excision by the endonuclease XPG. DNA from 93 patients with synovial sarcomas, myxoid liposarcomas, dermatofibrosarcomas protuberans (DFSP), malignant fibrous histiocytomas and leiomyosarcomas were genotyped for both XPD Lys751Gln and XPG Asp1104His polymorphisms. Departure from Hardy-Weinberg was highly significant for the XPG polymorphism with an excess of heterozygotes in synovial sarcomas (p = 1.5 x 10(-5)), myxoid liposarcomas (p = 1.5 x 10(-4)) and to a lesser extent in DFSP (p = 0.028). In the case of XPD, a significant deviation was observed in synovial sarcomas (p = 3 x 10(-6)) and DFSP (p = 0.0014). When tumors were pooled according to their genetic alterations, the proportion of carriers of the variant XPG allele was significantly increased in sarcomas with specific translocations as compared to sarcomas with complex genetics (p < 10(-9)). No difference was found for XPD. Genotyping of the tumor samples in synovial sarcomas and myxoid liposarcomas revealed frequent loss of heterozygosity for XPG, mostly due to the loss of the frequent allele. For XPD, both alleles were lost with a similar frequency. Our results raise the potential implication of the XPG Asp1104His polymorphism in the occurrence of chromosomal translocations associated with specific subtypes of sarcomas.
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PMID:Genetic polymorphisms of the XPG and XPD nucleotide excision repair genes in sarcoma patients. 1664 69

The structure-specific endonuclease XPG is an indispensable core protein of the nucleotide excision repair (NER) machinery. XPG cleaves the DNA strand at the 3' side of the DNA damage. XPG binding stabilizes the NER preincision complex and is essential for the 5' incision by the ERCC1/XPF endonuclease. We have studied the dynamic role of XPG in its different cellular functions in living cells. We have created mammalian cell lines that lack functional endogenous XPG and stably express enhanced green fluorescent protein (eGFP)-tagged XPG. Life cell imaging shows that in undamaged cells XPG-eGFP is uniformly distributed throughout the cell nucleus, diffuses freely, and is not stably associated with other nuclear proteins. XPG is recruited to UV-damaged DNA with a half-life of 200 s and is bound for 4 min in NER complexes. Recruitment requires functional TFIIH, although some TFIIH mutants allow slow XPG recruitment. Remarkably, binding of XPG to damaged DNA does not require the DDB2 protein, which is thought to enhance damage recognition by NER factor XPC. Together, our data present a comprehensive view of the in vivo behavior of a protein that is involved in a complex chromatin-associated process.
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PMID:Recruitment of the nucleotide excision repair endonuclease XPG to sites of UV-induced dna damage depends on functional TFIIH. 1700 Jul 69

Mildly affected individuals from xeroderma pigmentosum complementation group G (XP-G) possess single amino acid substitutions in the XPG protein that adversely affects its 3' endonuclease function in nucleotide excision repair. More serious mutations in the XPG gene generate truncated or unstable XPG proteins and result in a particularly early and severe form of the combined XP/CS complex. Following UV irradiation, cells from such XP-G/CS patients enter apoptosis more readily than other DNA repair-deficient cells. Here, we explore the mechanisms by which UV triggers the apoptotic cell death program in XP-G and XP-G/CS primary fibroblasts. Activation of the CD95 signalling pathway occurs within minutes and it is the earliest detectable post-UV event in such cells. This is rapidly followed by activation of caspase-8 then caspase-3. Several hours later caspase-9 becomes activated and the mitochondrial membrane potential drops, but without any obvious prior release of cytochrome c. Although p53 accumulates in XPG-deficient cells after UV irradiation, use of RNA interference demonstrates that p53 is not required for their UV-induced apoptotic response. p53 ablation of wild-type fibroblasts reduces MDM2 mRNA levels, inhibits accumulation of the 90kDa/92kDa Mdm2 isoforms, and prevents the nuclear relocalisation of Mdm2 after UV treatment. The same post-UV effects occur in XPG-deficient cells that express normal p53 levels. These results emphasise the importance of the extrinsic apoptotic pathway and aberrant Mdm2 events for the severe UV-induced apoptosis of XPG-deficient primary fibroblasts. XP-G/CS cells constitutively overexpress the pro-apoptotic Bax protein and a long isoform of the E2F1 transcription factor that controls S phase entry, which may prime them to enter apoptosis very readily after UV irradiation.
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PMID:UV-induced apoptosis in XPG-deficient fibroblasts involves activation of CD95 and caspases but not p53. 1720 56

DNA methylation is an epigenetic modification that is essential for gene silencing and genome stability in many organisms. Although methyltransferases that promote DNA methylation are well characterized, the molecular mechanism underlying active DNA demethylation is poorly understood and controversial. Here we show that Gadd45a (growth arrest and DNA-damage-inducible protein 45 alpha), a nuclear protein involved in maintenance of genomic stability, DNA repair and suppression of cell growth, has a key role in active DNA demethylation. Gadd45a overexpression activates methylation-silenced reporter plasmids and promotes global DNA demethylation. Gadd45a knockdown silences gene expression and leads to DNA hypermethylation. During active demethylation of oct4 in Xenopus laevis oocytes, Gadd45a is specifically recruited to the site of demethylation. Active demethylation occurs by DNA repair and Gadd45a interacts with and requires the DNA repair endonuclease XPG. We conclude that Gadd45a relieves epigenetic gene silencing by promoting DNA repair, which erases methylation marks.
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PMID:Gadd45a promotes epigenetic gene activation by repair-mediated DNA demethylation. 1726 71

Drosophila melanogaster XPG-like endonuclease (DmGEN) is a new category of nuclease belonging to the RAD2/XPG family. The DmGEN protein has two nuclease domains (N and I domains) similar to XPG/class I nucleases; however, unlike class I nucleases, in DmGEN these two nuclease domains are positioned close to each other as in FEN-1/class II and EXO-1/class III nucleases. To confirm the properties of DmGEN, we characterized the active-site mutant protein (E143A E145A) and found that DmGEN had flap endonuclease activity. DmGEN possessed weak nick-dependent 5'-3' exonuclease activity. Unlike XPG, DmGEN could not incise the bubble structure. Interestingly, based on characterization of flap endonuclease activity, DmGEN preferred the blocked-flap structure as a substrate. This feature is distinctly different from FEN-1. Furthermore, DmGEN cleaved the lagging strand of the model replication fork. Immunostaining revealed that DmGEN was present in the nucleus of actively proliferating Drosophila embryos. Thus, our studies revealed that DmGEN belongs to a new class (class IV) of the RAD2/XPG nuclease family. The biochemical properties of DmGEN and its possible role are also discussed.
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PMID:DmGEN shows a flap endonuclease activity, cleaving the blocked-flap structure and model replication fork. 1761 65


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