共查询到20条相似文献,搜索用时 62 毫秒
1.
目的 核酸酶介导的DNA双链末端切割对同源重组修复至关重要。然而,DNA末端构型对RecJ 5’-3’核酸外切酶活性的调控尚不清楚。本研究旨在探究DNA3’端和5’端构型对RecJ核酸外切酶活性的影响及其机制。方法 为探究DNA3’端构型对RecJ核酸外切酶活性的影响,使用含有Mg2+的体系,对具有不同3’突出末端长度(9 nt与18 nt)和3’突出末端修饰(磷酸化和硫代磷酸酯修饰)的单链DNA分别进行RecJ核酸酶活性检测。为揭示DNA 3’端构型对RecJ外切酶活性的调控机制,在Mg2+缺失的体系中,使RecJ与底物结合后进行凝胶迁移实验(EMSA)。为探索其他调控因子与DNA3’端构型对RecJ的协同作用,分别检测5’端磷酸化修饰和单链DNA结合蛋白(SSB)对DNA3’突出末端修饰的影响。结果 DNA3’端构型包括突出末端的长度和修饰(磷酸化和硫代磷酸酯修饰)均会抑制RecJ外切酶活性。DNA 3’端磷酸化和硫代磷酸酯修饰通过重塑RecJ-DNA的结合模式抑制RecJ外切酶活性。DNA 5’端磷酸化修饰可增强RecJ对具有不同3’端... 相似文献
2.
Single-stranded DNA (ssDNA)-binding protein (SSB) plays an important role in DNA replication, recombination, and repair. SSB consists of an N-terminal ssDNA-binding domain with an oligonucleotide/oligosaccharide binding fold and a flexible C-terminal tail involved in protein-protein interactions. SSB from Helicobacter pylori (HpSSB) was isolated, and the ssDNA-binding characteristics of HpSSB were analyzed by fluorescence titration and electrophoretic mobility shift assay. Tryptophan fluorescence quenching was measured as 61%, and the calculated cooperative affinity was 5.4 × 107 M− 1 with an ssDNA-binding length of 25-30 nt. The crystal structure of the C-terminally truncated protein (HpSSBc) in complex with 35-mer ssDNA [HpSSBc-(dT)35] was determined at a resolution of 2.3 Å. The HpSSBc monomer folds as an oligonucleotide/oligosaccharide binding fold with a Y-shaped conformation. The ssDNA wrapped around the HpSSBc tetramer through a continuous binding path comprising five essential aromatic residues and a positively charged surface formed by numerous basic residues. 相似文献
3.
Identification of the SSB Binding Site on E. coli RecQ Reveals a Conserved Surface for Binding SSB's C Terminus 总被引:1,自引:0,他引:1
RecQ DNA helicases act in conjunction with heterologous partner proteins to catalyze DNA metabolic activities, including recombination initiation and stalled replication fork processing. For the prototypical Escherichia coli RecQ protein, direct interaction with single-stranded DNA-binding protein (SSB) stimulates its DNA unwinding activity. Complex formation between RecQ and SSB is mediated by the RecQ winged-helix domain, which binds the nine C-terminal-most residues of SSB, a highly conserved sequence known as the SSB-Ct element. Using nuclear magnetic resonance and mutational analyses, we identify the SSB-Ct binding pocket on E. coli RecQ. The binding site shares a striking electrostatic similarity with the previously identified SSB-Ct binding site on E. coli exonuclease I, although the SSB binding domains in the two proteins are not otherwise related structurally. Substitutions that alter RecQ residues implicated in SSB-Ct binding impair RecQ binding to SSB and SSB/DNA nucleoprotein complexes. These substitutions also diminish SSB-stimulated DNA helicase activity in the variants, although additional biochemical changes in the RecQ variants indicate a role for the winged-helix domain in helicase activity beyond SSB protein binding. Sequence changes in the SSB-Ct element are sufficient to abolish interaction with RecQ in the absence of DNA and to diminish RecQ binding and helicase activity on SSB/DNA substrates. These results support a model in which RecQ has evolved an SSB-Ct binding site on its winged-helix domain as an adaptation that aids its cellular functions on SSB/DNA nucleoprotein substrates. 相似文献
4.
Kyung Suk Lee Amanda B. Marciel Alexander G. Kozlov Charles M. Schroeder Timothy M. Lohman Taekjip Ha 《Journal of molecular biology》2014
Single-stranded DNA binding proteins (SSBs) selectively bind single-stranded DNA (ssDNA) and facilitate recruitment of additional proteins and enzymes to their sites of action on DNA. SSB can also locally diffuse on ssDNA, which allows it to quickly reposition itself while remaining bound to ssDNA. In this work, we used a hybrid instrument that combines single-molecule fluorescence and force spectroscopy to directly visualize the movement of Escherichia coli SSB on long polymeric ssDNA. Long ssDNA was synthesized without secondary structure that can hinder quantitative analysis of SSB movement. The apparent diffusion coefficient of E. coli SSB thus determined ranged from 70,000 to 170,000 nt2/s, which is at least 600 times higher than that determined from SSB diffusion on short ssDNA oligomers, and is within the range of values reported for protein diffusion on double-stranded DNA. Our work suggests that SSB can also migrate via a long-range intersegment transfer on long ssDNA. The force dependence of SSB movement on ssDNA further supports this interpretation. 相似文献
5.
The stability and deletion-size-distribution profiles of leading strand (CAG)75 and (CTG)137 trinucleotide repeat arrays inserted in the Escherichia coli chromosome were investigated upon overexpression of the single-stranded DNA-binding protein (SSB) and in mutant strains deficient for the SbcCD (Rad51/Mre11) nuclease. SSB overexpression increases the stability of the (CAG)75 repeat array and leads to a loss of the bias towards large deletions for the same array. Furthermore, the absence of SbcCD leads to a reduction in the number of large deletions in strains containing the (CTG)137 repeat array. 相似文献
6.
Edwin Antony Elizabeth Weiland Quan Yuan Carol M. Manhart Binh Nguyen Alexander G. Kozlov Charles S. McHenry Timothy M. Lohman 《Journal of molecular biology》2013
Escherichia coli single-stranded DNA binding protein (SSB) plays essential roles in DNA replication, recombination and repair. SSB functions as a homotetramer with each subunit possessing a DNA binding domain (OB-fold) and an intrinsically disordered C-terminus, of which the last nine amino acids provide the site for interaction with at least a dozen other proteins that function in DNA metabolism. To examine how many C-termini are needed for SSB function, we engineered covalently linked forms of SSB that possess only one or two C-termini within a four-OB-fold “tetramer”. Whereas E. coli expressing SSB with only two tails can survive, expression of a single-tailed SSB is dominant lethal. E. coli expressing only the two-tailed SSB recovers faster from exposure to DNA damaging agents but accumulates more mutations. A single-tailed SSB shows defects in coupled leading and lagging strand DNA replication and does not support replication restart in vitro. These deficiencies in vitro provide a plausible explanation for the lethality observed in vivo. These results indicate that a single SSB tetramer must interact simultaneously with multiple protein partners during some essential roles in genome maintenance. 相似文献
7.
Michael L. Rolfsmeier 《Journal of molecular biology》2010,397(1):31-498
Homologous recombination is an important pathway in the repair of DNA double-strand breaks in all organisms. In mesophiles, single-stranded DNA binding proteins (SSBs) are believed to be involved in the removal of single-stranded DNA (ssDNA) secondary structure during the presynaptic step of homologous recombination, facilitating the formation of a contiguous Rad51/RecA nucleoprotein filament. Here we report a role for the thermophilic archaeal Sulfolobus solfataricus SSB (SsoSSB) in the presynaptic step of homologous recombination. We have identified multiple quaternary structural forms of this protein in vivo and examined the activity of SsoSSB with the strand-exchange protein S. solfataricus RadA (SsoRadA). Using gel-shift analysis, we found that the two major forms of SsoSSB have different DNA binding affinities and site sizes. Biochemical examination of the monomeric form of SsoSSB suggests that it has a minor role in presynapsis and may slightly inhibit the ssDNA-dependent ATPase activity of SsoRadA. The tetrameric form of SsoSSB, however, significantly inhibits SsoRadA ssDNA-dependent ATPase activity under both saturating and subsaturating conditions. Order-of-addition experiments indicate that preincubation of tetrameric SsoSSB and SsoRadA prior to reaction initiation with ssDNA relieves the inhibition observed when SsoSSB is added either before or after SsoRadA. In addition, we demonstrate a direct interaction between SsoRadA and SsoSSB using coimmunoprecipitation. Taken together, these results suggest that a direct interaction between SsoSSB and SsoRadA may occur in vivo prior to the formation of the SsoRadA nucleoprotein filament. 相似文献
8.
RecJ exonuclease: substrates, products and interaction with SSB 总被引:4,自引:0,他引:4
Han ES Cooper DL Persky NS Sutera VA Whitaker RD Montello ML Lovett ST 《Nucleic acids research》2006,34(4):1084-1091
The RecJ exonuclease from Escherichia coli degrades single-stranded DNA (ssDNA) in the 5′–3′ direction and participates in homologous recombination and mismatch repair. The experiments described here address RecJ's substrate requirements and reaction products. RecJ complexes on a variety of 5′ single-strand tailed substrates were analyzed by electrophoretic mobility shift in the absence of Mg2+ ion required for substrate degradation. RecJ required single-stranded tails of 7 nt or greater for robust binding; addition of Mg2+ confirmed that substrates with 5′ tails of 6 nt or less were poor substrates for RecJ exonuclease. RecJ is a processive exonuclease, degrading ~1000 nt after a single binding event to single-strand DNA, and releases mononucleotide products. RecJ is capable of degrading a single-stranded tail up to a double-stranded junction, although products in such reactions were heterogeneous and RecJ showed a limited ability to penetrate the duplex region. RecJ exonuclease was equally potent on 5′ phosphorylated and unphosphorylated ends. Finally, DNA binding and nuclease activity of RecJ was specifically enhanced by the pre-addition of ssDNA-binding protein and we propose that this specific interaction may aid recruitment of RecJ. 相似文献
9.
Summary We examined the possibility that the recA441 mutation, which partially suppresses the UV sensitivity of uvr recF mutant bacteria, exerts its effect by coding for an altered RecA protein that competes more efficiently than the RecA+ protein with SSB for ssDNA in vivo. Using an assay measuring recombination between UV-damaged DNA and intact homologous DNA, we found that the introduction of the recA441 mutation partially suppressed the defects in recombination in bacteria lacking RecF activity but not in bacteria with excess SSB, although recombination was affected more in recF mutants than in bacteria overproducing SSB. These results therefore do not support the hypothesis that RecA441 protein, or RecA protein with the help of RecF protein, is required during recombination of UV-damaged DNA to compete with SSB for ssDNA. 相似文献
10.
María del Rosario Espinoza-Mellado Edgar Oliver López-Villegas Ramón I Arteaga-Garibay Silvia Giono-Cerezo 《Memórias do Instituto Oswaldo Cruz》2013,108(8):1074-1077
Haemophilus influenzae belongs to respiratory tract microbiota. We
observed vacuoles formation in previous studies with H. influenzae
culture supernatants, so in this work we characterised that cytotoxic effect. We
observed an abundant production of acidic cytoplasmic vacuoles due to the presence of
a “vacuolating factor” in H. influenzae supernatants which was characterised as
thermolabile. Greatest vacuolating activity was observed when utilizing the fraction
> 50 kDa. The presence of a large number of vacuoles in HEp-2 cells was verified
by transmission electron microscopy and some vacuoles were identified with a double
membrane and/or being surrounded by ribosomes. These results suggest similar
behaviour to that of vacuolating effects described by autotransporter proteins an
undescribed cytotoxic effect induced by H. influenzae . 相似文献
11.
Ralph R. Meyer Daniel W. Voegele Steven M. Ruben Diane C. Rein John M. Trela 《Mutation research》1982,94(2):299-313
Two ssb mutants of Escherichia coli, whic carry a lesion in the single-strand DNA-binding protein (SSB), are sensitive to UV-irradiation. We have investigated the influence of SSB on the “SOS” repair pathway by examining the levels of recA protein synthesis. These strains fail to induced normal levels of recA protein after treatment with nalidixic acid or ultraviolet light. The level of recA protein synthesis in wild-type cells is about three times greater than ssb cells. This deficiency in ssb mutants occurs in all strains and at all temperatures tested (30–41.5°). In contrast, the ssb-1 mutant has no effect on temperature-induced recA induction in a recA441 (tif-1) strain. Cells carrying ssb+ plasmids and overproducing normal DNA-binding protein surprisingly are moderated UV-sensitive and have reduced levels of recA protein synthesis. Together these results establish that single-strand DNA-binding protein is involved in the induction of recA, and accounts, at least in part, for the UV sensivitiy of ssb mutant. Three possible mechanisms to explain the role of SSB are discussed. 相似文献
12.
Michal R. Szymanski 《Journal of molecular biology》2010,398(1):8-9183
Quantitative analysis of the interactions of the Escherichia coli primosomal PriB protein with a single-stranded DNA was done using quantitative fluorescence titration, photocrosslinking, and analytical ultracentrifugation techniques. Stoichiometry studies were done with a series of etheno-derivatives of single-stranded (ss) DNA oligomers. Interactions with the unmodified nucleic acids were studied, using the macromolecular competition titration (MCT) method. The total site-size of the PriB dimer-ssDNA complex, i.e. the maximum number of nucleotides occluded by the PriB dimer in the complex, is 12 ± 1 nt. The protein has a single DNA-binding site, which is located centrally within the dimer and has a functionally homogeneous structure. The stoichiometry and photocrosslinking data show that only a single monomer of the PriB dimer engages in interactions with the nucleic acid. The analysis of the PriB binding to long oligomers was done using a statistical thermodynamic model that takes into account the overlap of potential binding sites and cooperative interactions. The PriB dimer binds the ssDNA with strong positive cooperativity. Both the intrinsic affinity and cooperative interactions are accompanied by a net ion release, with anions participating in the ion exchange process. The intrinsic binding process is an entropy-driven reaction, suggesting strongly that the DNA association induces a large conformational change in the protein. The PriB protein shows a dramatically strong preference for the homo-pyrimidine oligomers with an intrinsic affinity higher by about three orders of magnitude, as compared to the homo-purine oligomers. The significance of these results for PriB protein activity is discussed. 相似文献
13.
Saikrishnan K Jeyakanthan J Venkatesh J Acharya N Sekar K Varshney U Vijayan M 《Journal of molecular biology》2003,331(2):385-393
Single-stranded DNA-binding protein (SSB) is an essential protein necessary for the functioning of the DNA replication, repair and recombination machineries. Here we report the structure of the DNA-binding domain of Mycobacterium tuberculosis SSB (MtuSSB) in four different crystals distributed in two forms. The structure of one of the forms was solved by a combination of isomorphous replacement and anomalous scattering. This structure was used to determine the structure of the other form by molecular replacement. The polypeptide chain in the structure exhibits the oligonucleotide binding fold. The globular core of the molecule in different subunits in the two forms and those in Escherichia coli SSB (EcoSSB) and human mitochondrial SSB (HMtSSB) have similar structure, although the three loops exhibit considerable structural variation. However, the tetrameric MtuSSB has an as yet unobserved quaternary association. This quaternary structure with a unique dimeric interface lends the oligomeric protein greater stability, which may be of significance to the functioning of the protein under conditions of stress. Also, as a result of the variation in the quaternary structure the path adopted by the DNA to wrap around MtuSSB is expected to be different from that of EcoSSB. 相似文献
14.
15.
Wei T Zhang S Zhu S Sheng D Ni J Shen Y 《Biochemical and biophysical research communications》2008,367(3):523-529
NurA is a novel 5′-3′ exonuclease that is closely linked to Mre11 and Rad50 homologues in most thermophilic archaea. We report a physical and functional interaction between NurA (StoNurA) and single-stranded DNA-binding protein (StoSSB) from the hyperthermophilic archaeon Sulfolobus tokodaii. StoSSB was identified as a novel StoNurA-interacting protein by pull-down assay using Ni-NTA agarose beads and MALDI-TOF mass spectrometry. The direct interaction between StoNurA and StoSSB was further confirmed by yeast two-hybrid and co-immunoprecipitation analysis. The interaction was supposed to have functional significance because it was found that StoSSB inhibited the 5′-3′ ssDNA and dsDNA exonuclease and ssDNA endonuclease activities of StoNurA. Our results suggest that NurA may function closely together with SSB in DNA transactions in archaea. 相似文献
16.
Homologous recombination is a crucial process for the maintenance of genome integrity. The two main recombination pathways in Escherichia coli (RecBCD and RecF) differ in the initiation of recombination. The RecBCD enzyme is the only component of the RecBCD pathway which acts in the initiation of recombination, and possesses all biochemical activities (helicase, 5′-3′ exonuclease, χ cutting and loading of the RecA protein onto single-stranded (ss) DNA) needed for the processing of double stranded (ds) DNA breaks (DSB). When the nuclease and RecA loading activities of the RecBCD enzyme are inactivated, the proteins of the RecF recombination machinery, i.e., RecJ and RecFOR substitute for the missing 5′-3′ exonuclease and RecA loading activity respectively. The above mentioned activities of the RecBCD enzyme are regulated by an octameric sequence known as the χ site (5′-GCTGGTGG-3′). One class of recC mutations, designated recC*, leads to reduced χ cutting in vitro. The recC1004 strain (a member of the recC* mutant class) is recombination proficient and resistant to UV radiation. In this paper, we studied the effects of mutations in RecF pathway genes on DNA repair (after UV and γ radiation) and on conjugational recombination in recC1004 and recC1004 recD backgrounds. We found that DNA repair after UV and γ radiation in the recC1004 and recC1004 recD backgrounds depends on recFOR and recJ gene products. We also showed that the recC1004 mutant has reduced survival after γ radiation. This phenotype is suppressed by the recD mutation which abolishes the RecBCD dependent nuclease activity. Finally, the genetic requirements for conjugational recombination differ from those for DNA repair. Conjugational recombination in recC1004 recD mutants is dependent on the recJ gene product. Our results emphasize the importance of the canonical χ recognition activity in DSB repair and the significance of interchange between the components of two recombination machineries in achieving efficient DNA repair. 相似文献
17.
Claire A. Adams Manana Melikishvili David W. Rodgers Anthony E. Pegg 《Journal of molecular biology》2009,389(2):248-1202
The mutagenic and cytotoxic effects of many alkylating agents are reduced by O6-alkylguanine-DNA alkyltransferase (AGT). In humans, this protein not only protects the integrity of the genome, but also contributes to the resistance of tumors to DNA-alkylating chemotherapeutic agents. Here we describe and test models for cooperative multiprotein complexes of AGT with single-stranded and duplex DNAs that are based on in vitro binding data and the crystal structure of a 1:1 AGT-DNA complex. These models predict that cooperative assemblies contain a three-start helical array of proteins with dominant protein-protein interactions between the amino-terminal face of protein n and the carboxy-terminal face of protein n + 3, and they predict that binding duplex DNA does not require large changes in B-form DNA geometry. Experimental tests using protein cross-linking analyzed by mass spectrometry, electrophoretic and analytical ultracentrifugation binding assays, and topological analyses with closed circular DNA show that the properties of multiprotein AGT-DNA complexes are consistent with these predictions. 相似文献
18.
Shao J Zhang J Kowal P Lu Y Wang PG 《Biochemical and biophysical research communications》2002,295(1):1-8
The lipopolysaccharide of capsule deficient Haemophilus influenzae strain Rd contains an N-acetylgalactosamine residue attached to the terminal globotriose moiety in the Hex5 glycoform. Genome analysis identified an open reading frame HI1578, referred to as lgtD, whose amino acid sequence shows significant level of similarity to a number of bacterial glycosyltransferases involved in lipopolysaccharide biosynthesis. To investigate its function, overexpression and biochemical characterization were performed. Most of the protein was obtained in a highly soluble and active form. By using standard glycosyltransferase assay and HPLC, we show that LgtD is an N-acetylgalactosaminyltransferase with high donor substrate specificity and globotriose is a highly preferred acceptor substrate for the enzyme. The Km for UDP-GalNAc and globotriose are 58 μM and 8.6 mM, respectively. The amino acid sequence of the enzyme shows the conserved features of family II glycosyltransferases. This is the first N-acetylgalactosaminyltransferase identified from H. influenzae, which shows potential application in large-scale synthesis of globo-series oligosaccharides. 相似文献
19.
Taisuke Wakamatsu Yoshiaki Kitamura Yutaro Kotera Noriko Nakagawa Seiki Kuramitsu Ryoji Masui 《The Journal of biological chemistry》2010,285(13):9762-9769
RecJ is a single-stranded DNA (ssDNA)-specific 5′-3′ exonuclease that plays an important role in DNA repair and recombination. To elucidate how RecJ achieves its high specificity for ssDNA, we determined the entire structures of RecJ both in a ligand-free form and in a complex with Mn2+ or Mg2+ by x-ray crystallography. The entire RecJ consists of four domains that form a molecule with an O-like structure. One of two newly identified domains had structural similarities to an oligonucleotide/oligosaccharide-binding (OB) fold. The OB fold domain alone could bind to DNA, indicating that this domain is a novel member of the OB fold superfamily. The truncated RecJ containing only the core domain exhibited much lower affinity for the ssDNA substrate compared with intact RecJ. These results support the hypothesis that these structural features allow specific binding of RecJ to ssDNA. In addition, the structure of the RecJ-Mn2+ complex suggests that the hydrolysis reaction catalyzed by RecJ proceeds through a two-metal ion mechanism. 相似文献
20.
Kae Sueda Ayano Meguro Takeshi Uchida Jun-ichi Inaba Chikara Masuta 《FEBS letters》2010,584(5):945-950
The RNA silencing suppressor 2b protein of Cucumber mosaic virus (CMV) is difficult to produce in Escherichia coli. We compared two CMV 2b proteins that differ in their toxicity against E. coli and found that the acidic amino acid residues in the C-terminal significantly affected the toxicity and expression level of the protein in E. coli. In addition, in a DNA-binding assay, 2b had the ability to bind to DNA, and this ability was affected by the charge on the C-terminal residues of 2b. We concluded that the C-terminal residues were important for 2b’s DNA-binding ability, which may partly explain the toxicity of the protein. 相似文献