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

---

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

The RAD2 family of nucleases includes human XPG (Class I), FEN1 (Class II), and HEX1/hEXO1 (Class III) products gene. These proteins exhibit a blend of substrate specific exo- and endonuclease activities and contribute to repair, recombination, and/or replication. To date, the substrate preferences of the EXO1-like Class III proteins have not been thoroughly defined. We report here that the RAD2 domain of human exonuclease 1 (HEX1-N2) exhibits both a robust 5' to 3' exonuclease activity on single- and double-stranded DNA substrates as well as a flap structure-specific endonuclease activity but does not show specific endonuclease activity at 10-base pair bubble-like structures, G:T mismatches, or uracil residues. Both the 5' to 3' exonuclease and flap endonuclease activities require a divalent metal cofactor, with Mg(2+) being the preferred metal ion. HEX1-N2 is approximately 3-fold less active in Mn(2+)-containing buffers and exhibits <5% activity in the presence of Co(2+), Zn(2+), or Ca(2+). The optimal pH range for the nuclease activities of HEX1-N2 is 7.2-8.2. The specific activity of its 5' to 3' exonuclease function is 2.5-7-fold higher on blunt end and 5'-recessed double-stranded DNA substrates compared with duplex 5'-overhang or single-stranded DNAs. The flap endonuclease activity of HEX1-N2 is similar to that of human flap endonuclease-1, both in terms of turnover efficiency (k(cat)) and site of incision, and is as efficient (k(cat)/K(m)) as its exonuclease function. The nuclease activities of HEX1-N2 described here indicate functions for the EXO1-like proteins in replication, repair, and/or recombination that may overlap with human flap endonuclease-1.
...
PMID:The RAD2 domain of human exonuclease 1 exhibits 5' to 3' exonuclease and flap structure-specific endonuclease activities. 1060 37

Hereditary Nonpolyposis Colorectal Cancer (HNPCC) is a genetically heterogeneous disorder caused by germ-line mutations in one of several DNA mismatch repair (MMR) genes, most commonly in hMSH2 and hMLH1. Human exonuclease 1 (hExo1) possesses both 5'exonuclease and flap endonuclease activities and plays a role in DNA repair, recombination, and replication. The enzyme interacts with MMR proteins, hMsh2, hMlh1, and hMsh3. Recently, eight missense mutations in hEXO1 were identified in atypical HNPCC patients, who have been screened to be negative for hMSH2, hMLH1, and hMSH6 mutations. To address the question of whether these mutations cause susceptibility to HNPCC, in vitro nuclease activity and protein-protein interaction assays were performed in this study. We found that two mutants, E109K and L410R, lost their exonuclease activities while retaining their capacity to bind to the DNA substrate. Three other mutants, P640S, G759E, and P770L, displayed a reduced capacity to interact with hMsh2. The combination of these three point mutations leads to the binding capacity with hMsh2 to nearly zero. Evidence made available in this study sheds light on the pathogenesis of HNPCC, perhaps initiated by an additional MMR gene, hEXO1.
...
PMID:Functional alterations of human exonuclease 1 mutants identified in atypical hereditary nonpolyposis colorectal cancer syndrome. 1241 23

HEX1/hExo1 is a Class III nuclease of the RAD2 family with 5' to 3' exonuclease and flap structure-specific endonuclease activities. HEX1/hExo1 is expressed at low levels in a wide variety of tissues, but at higher levels in fetal liver and adult bone marrow, suggesting HEX1/hExo1 is important for hematopoietic stem cell development. A putative HEX1/hExo1 promoter fragment extending from -6240 to +1600bp exhibits cell-type specific activity in transient transfection assays. This fragment directs high luciferase reporter gene expression in the hematopoietic cell line K562, chronic myelogenous leukemia cells, but low luciferase expression in the non-hematopoietic cell line HeLa, human cervical carcinoma cells. Deletion studies identified a fragment spanning -688 to +1600bp that exhibits full transcriptional activity while a slightly shorter fragment from -658 to +1600bp exhibits significantly decreased promoter activity. In vitro binding assays revealed DNA-binding activities that interact with -687 to -681bp and -665 to -658bp elements. Oligonucleotide competition and antibody disruption studies determined that the transcription factor CREB-1 recognizes the -687 to -681bp element, while transcription factors Sp1 and Sp3 recognize the -665 to -658bp element. Mutation of either the CREB-1 or Sp1/Sp3 binding sites dramatically reduces HEX1/hExo1 promoter activity and elimination of both elements abolishes promoter activity.
...
PMID:Identification of the human HEX1/hExo1 gene promoter and characterization of elements responsible for promoter activity. 1253 89

A novel endonuclease, a new member of the RAD2 nuclease family, has been identified from the higher plant, rice (Oryza sativa L. cv. Nipponbare), and designated as OsSEND-1. The open reading frame of the OsSEND-1 cDNA encoded a predicted product of 641 amino acid residues with a molecular weight of 69.9 kDa. The encoded protein showed a relatively high degree of sequence homology with the RAD2 nuclease family proteins, especially RAD2 nuclease, but it differed markedly from FEN-1, XPG or HEX1/EXO1. The N- and I-domains in the family were highly conserved in the OsSEND-1 sequence. The protein was much smaller than XPG, but larger than HEX1/EXO1 and FEN-1. The genome sequence was composed of 14 exons, and was localized at the almost terminal region of the short arm of chromosome 8. Northern blotting and in situ hybridization analyses demonstrated preferential expression of OsSEND-1 mRNA in proliferating tissues such as meristem. The mRNA level of OsSEND-1 was induced by UV and DNA-damaging agent such as MMS or H2O2, indicating that OsSEND-1 has some roles in the repair of many types of damaged DNA. The recombinant peptide showed endonuclease activity.
...
PMID:OsSEND-1: a new RAD2 nuclease family member in higher plants. 1260 91

Rad2 family nucleases, identified by sequence similarity within their catalytic domains, function in multiple pathways of DNA metabolism. Three members of the Saccharomyces cerevisiae Rad2 family, Rad2, Rad27, and exonuclease 1 (Exo1), exhibit both 5' exonuclease and flap endonuclease activities. Deletion of RAD27 results in defective Okazaki fragment maturation, DNA repair, and subsequent defects in mutation avoidance and chromosomal stability. However, strains lacking Rad27 are viable. The expression profile of EXO1 during the cell cycle is similar to that of RAD27 and other genes encoding proteins that function in DNA replication and repair, suggesting Exo1 may function as a back up nuclease for Rad27 in DNA replication. We show that overexpression of EXO1 suppresses multiple rad27 null mutation-associated phenotypes derived from DNA replication defects, including temperature sensitivity, Okazaki fragment accumulation, the rate of minichromosome loss, and an elevated mutation frequency. While generally similar findings were observed with RAD2, overexpression of RAD2, but not EXO1, suppressed the MMS sensitivity of the rad27 null mutant cells. This suggests that Rad2 can uniquely complement Rad27 in base excision repair (BER). Furthermore, Rad2 and Exo1 complemented the mutator phenotypes and cell cycle defects of rad27 mutant strains to differing extents, suggesting distinct in vivo nucleic acid substrates.
...
PMID:Complementary functions of the Saccharomyces cerevisiae Rad2 family nucleases in Okazaki fragment maturation, mutation avoidance, and chromosome stability. 1289 88

In kinetoplastid protists, maturation of mitochondrial pre-mRNAs involves the insertion and deletion of uridylates (Us) within coding regions, as specified by mitochondrial DNA-encoded guide RNAs. U-deletion editing involves endonucleolytic cleavage of the pre-mRNA at the editing site followed by U-specific 3'-5'-exonucleolytic removal of nonbase-paired Us prior to ligation of the two mRNA cleavage fragments. We showed previously that an exonuclease/endonuclease/phosphatase (EEP) motif protein from Leishmania major, designated RNA editing exonuclease 1 (REX1) (Kang, X., Rogers, K., Gao, G., Falick, A. M., Zhou, S.-L., and Simpson, L. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 1017-1022), exhibits 3'-5'-exonuclease activity. Two EEP motif proteins have also been identified in the Trypanosoma brucei editing complex. TbREX1 is a homologue of LmREX1, and TbREX2 shows homology to another editing protein in L. major, which lacks the EEP motif (LmREX2*). Here we have expressed the T. brucei EEP motif proteins in insect cells and purified them to homogeneity. We showed that these are U-specific 3'-5'-exonucleases that are inhibited by base pairing of 3' Us. The recombinant EEP motif alone also showed 3'-5' U-specific exonuclease activity, and mutations of the REX EEP motifs greatly reduced exonuclease activity. The absence of enzymatic activity in LmREX2* was confirmed with a purified recombinant protein. We showed that pre-cleaved U-deletion editing could be reconstituted with either TbREX1 or TbREX2 in combination with either RNA ligase, LmREL1, or LmREL2. Down-regulation of TbREX2 expression by conditional RNA interference had little effect on parasite viability or sedimentation of the L-complex, suggesting either that TbREX2 is inactive in vivo or that TbREX1 can compensate for the loss of TbREX2 function in down-regulated cells.
...
PMID:Uridylate-specific 3' 5'-exoribonucleases involved in uridylate-deletion RNA editing in trypanosomatid mitochondria. 1769 20

Eukaryotic exonuclease 1 functions in replication, recombination, mismatch repair, telomere maintenance, immunoglobulin (Ig) gene class switch recombination, and somatic hypermutation. The enzyme has 5'-3' exonuclease, flap endonuclease, and weak RNaseH activity in vitro, but it has been difficult to reconcile these activities with its diverse biological functions. We report robust cleavage by human exonuclease 1 of transcribed G-rich DNA sequences with potential to form G loops and G4 DNA. Predicted Ig switch recombination intermediates are substrates for both exonucleolytic and 5' flap endonucleolytic cleavage. Excision is nick-dependent and structure-dependent. These results lead to a model for exonuclease 1 function in class switch recombination in which cleavage at activation-induced deaminase (AID)-initiated nicks produces gaps that become substrates for further attack by AID and subsequent repair.
...
PMID:Activities of human exonuclease 1 that promote cleavage of transcribed immunoglobulin switch regions. 1894 Sep 26

Mismatch repair contributes to genetic stability, and inactivation of the mammalian pathway leads to tumor development. Mismatch correction occurs by an excision-repair mechanism and has been shown to depend on the 5' to 3' hydrolytic activity exonuclease 1 (Exo1) in eukaryotic cells. However, genetic and biochemical studies have indicated that one or more Exo1-independent modes of mismatch repair also exist. We have analyzed repair of nicked circular heteroduplex DNA in extracts of Exo1-deficient mouse embryo fibroblast cells. Exo1-independent repair under these conditions is MutL alpha-dependent and requires functional integrity of the MutL alpha endonuclease metal-binding motif. In contrast to the Exo1-dependent reaction, we have been unable to detect a gapped excision intermediate in Exo1-deficient extracts when repair DNA synthesis is blocked. A possible explanation for this finding has been provided by analysis of a purified system comprised of MutS alpha, MutL alpha, replication factor C, proliferating cell nuclear antigen, replication protein A, and DNA polymerase delta that supports Exo1-independent repair in vitro. Repair in this system depends on MutL alpha incision of the nicked heteroduplex strand and dNTP-dependent synthesis-driven displacement of a DNA segment spanning the mismatch. Such a mechanism may account, at least in part, for the Exo1-independent repair that occurs in eukaryotic cells, and hence the modest cancer predisposition of Exo1-deficient mammalian cells.
...
PMID:A possible mechanism for exonuclease 1-independent eukaryotic mismatch repair. 1942 Feb 20

Double-strand breaks (DSBs) in DNA are lethal unless repaired. Faithful repair requires processing of the DSB ends and interaction with intact homologous DNA, which can produce genetic recombinants. To determine the role of nucleases in DSB end-processing and joint molecule resolution, we studied recombination at the site of a single DSB, generated by induction of the I-SceI endonuclease, during meiosis of fission yeast lacking Rec12 (Spo11 homolog) and, hence, other DSBs. We find that in the presence of the MRN (Rad32-Rad50-Nbs1) complex efficient recombination requires Ctp1, the ortholog of the nuclease Sae2, but not the nuclease activity of MRN. In the absence of MRN, exonuclease 1 (Exo1) becomes the major nuclease required for efficient recombination. Our data indicate that MRN enables access of Ctp1 to the DSB but blocks access of Exo1. In our assay, the Rad16-Swi10 nuclease, required for nucleotide excision-repair, is required for efficient recombination, presumably to remove heterologous DNA at the end of the I-SceI cut site. Another nuclease, the Mus81-Eme1 Holliday junction resolvase, is required to generate crossovers accompanying gene conversion at the I-SceI cut site. Additional, previously published evidence indicates that these 5 nucleases play similar roles in wild-type fission yeast meiotic recombination and in the repair of spontaneous and damage-induced mitotic DSBs. We propose that in wild-type meiosis MRN, in conjunction with Ctp1, removes the covalently attached Rec12 protein from the DNA end, which is then resected by Ctp1 and other activities to produce the single-stranded DNA necessary for further steps of DSB repair.
...
PMID:Ctp1 and Exonuclease 1, alternative nucleases regulated by the MRN complex, are required for efficient meiotic recombination. 1947 Apr 80

Trinucleotide repeats can form stable secondary structures that promote genomic instability. To determine how such structures are resolved, we have defined biochemical activities of the related RAD2 family nucleases, FEN1 (Flap endonuclease 1) and EXO1 (exonuclease 1), on substrates that recapitulate intermediates in DNA replication. Here, we show that, consistent with its function in lagging strand replication, human (h) FEN1 could cleave 5'-flaps bearing structures formed by CTG or CGG repeats, although less efficiently than unstructured flaps. hEXO1 did not exhibit endonuclease activity on 5'-flaps bearing structures formed by CTG or CGG repeats, although it could excise these substrates. Neither hFEN1 nor hEXO1 was affected by the stem-loops formed by CTG repeats interrupting duplex regions adjacent to 5'-flaps, but both enzymes were inhibited by G4 structures formed by CGG repeats in analogous positions. Hydroxyl radical footprinting showed that hFEN1 binding caused hypersensitivity near the flap/duplex junction, whereas hEXO1 binding caused hypersensitivity very close to the 5'-end, correlating with the predominance of hFEN1 endonucleolytic activity versus hEXO1 exonucleolytic activity on 5'-flap substrates. These results show that FEN1 and EXO1 can eliminate structures formed by trinucleotide repeats in the course of replication, relying on endonucleolytic and exonucleolytic activities, respectively. These results also suggest that unresolved G4 DNA may prevent key steps in normal post-replicative DNA processing.
...
PMID:Complementary roles for exonuclease 1 and Flap endonuclease 1 in maintenance of triplet repeats. 2064 45


1 2 3 Next >>

---