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At least 703 records · Page 39Linked to original sources
PubMed1990

Design, synthesis, testing, and quantitative structure-activity relationship analysis of substituted salicylaldehyde Schiff bases of 1-amino-3-hydroxyguanidine tosylate as new antiviral agents against coronavirus.

Further modifications of the structural features of Schiff bases of hydroxyaminoguanidines (SB-HAG) led to nine substituted salicylaldehyde Schiff bases of HAG (SSB-HAG) derivatives and three other SB-HAG derivatives. These new compounds were tested for the first time against infection by a coronavirus, mouse hepatitis virus (MHV). The most active compound, 2 [1-[(3'-allyl-2'-hydroxybenzylidene)amino]- 3-hydroxyguanidine], against the growth of MHV is about 376 times more active than hydroxyguanidine and about 564 times more active than HAG itself when the TCID50 values are compared. Plaque assays of MHV released from cells treated with these compounds suggest that SSB-HAG tosylate may inhibit the transcription of viral RNAs in virus-infected cells. Quantitative structure-activity relationship (QSAR) analyses of two subsets show that the inhibitory activities correlate well with the electronic and the lipophilic parameters. The structural requirements for the antiviral activity of substituted SSB-HAG tosylate against coronaviral infection are stringent according to the inhibitory activities and QSAR analysis of these new compounds.

Aldehydes↗
PubMed2005

Comparison between X-ray photon and secondary electron damage to DNA in vacuum.

Both monolayer and thick (20 microm) films of dry pGEM-3Zf(-) plasmid DNA deposited on tantalum foil were exposed to Al Kalpha X-rays (1.5 keV) for various times in an ultrahigh vacuum chamber. For monolayer DNA, the damage was induced mainly by low energy secondary electrons (SEs) emitted from the tantalum. For the thick films, DNA damage was induced chiefly by X-ray photons. Different forms of plasmid DNA were separated and quantified by agarose gel electrophoresis. The exposure curves for the formation of nicked circular (single strand break, SSB), linear (double strand break, DSB), and interduplex cross-link forms 1 and 2 were obtained for both monolayer and thick films of DNA, respectively. The lower limits of G values for SSB and DSB induced by SEs were derived to be 86 +/- 2 and 8 +/- 2 nmol J(-1), respectively. These values are 1.5 and 1.6 times larger than those obtained with 1.5 keV photons. The projected X-ray energy dependence of the low energy electron (LEE) enhancement factor for the SSB and DSB in monolayer DNA is also discussed. This new method of investigation of the SE-induced damage to large biomolecules allows direct comparison of the yield of products induced by high energy photons and LEEs under identical experimental conditions.

Algorithms↗
PubMed1986

The effect of 2-[(aminopropyl)amino] ethanethiol (WR1065) on radiation-induced DNA damage and repair and cell progression in V79 cells.

The radioprotector 2-[(aminopropyl)amino] ethanethiol (WR1065) was investigated with respect to its ability to affect radiation-induced DNA damage and repair in V79 cells. Studies were performed to evaluate the protector under conditions in which it is known to be effective in reducing the cytotoxic and mutagenic effects of gamma-irradiation. At a concentration of 4 mM, WR1065 protected against the formation of single strand breaks (SSB), as determined by the method of alkaline elution, when it was present during irradiation. The protector appeared, however, to inhibit the subsequent postirradiation repair or rejoining of SSB. While repair was complete within 24 h, the protector reduced the rate of repair by a factor of 3. This inhibitory effect on the rate of repair did not correlate with either measured differences in cell survival or mutagenesis. The radioprotector was also investigated with respect to its ability to affect cell cycle progression. WR1065 present in the growth medium inhibited the progression of cells through S-phase, and cell-doubling time following a 3 h exposure to the protector was increased from 11 to 18 h. These data are consistent with the well characterized property of thiols to inhibit DNA polymerase activity. It was concluded that, while the presence of WR1065 during irradiation reduced SSB-DNA damage, its effect on the subsequent rejoining of these breaks could not be correlated with its observed effect on protecting against radiation-induced mutagenesis. It may be that the inhibition of cell-cycle progression by the protector allowed more time to enhance the fidelity of repair as measured by the protector's ability to protect against radiation-induced mutagenesis.

Animals↗
PubMed2002

Autoantibody in a patient with chronic hepatitis C virus infection showing complete remission after interferon therapy.

A 42-year-old woman was admitted to Kinashi Ohbayashi Hospital for liver dysfunction. She presented with hepatitis C viral infection accompanied by autoimmune hepatitis-like serological manifestations, such as antinuclear antibody (ANA), antismooth muscle cell antibody and especially anti-ribonucleoprotein (RNP) antibody and anti-SSB antibody. After interferon therapy, hepatitis C virus was not detected and ANA, anti-RNP antibody and anti-SSB antibody disappeared. To our knowledge, this is the first reported hepatitis C patient showing anti-RNP antibody and anti-SSB antibody, having complete remission after interferon therapy.

Adult↗
PubMed2001

Assembly of RecA-like recombinases: distinct roles for mediator proteins in mitosis and meiosis.

Members of the RecA family of recombinases from bacteriophage T4, Escherichia coli, yeast, and higher eukaryotes function in recombination as higher-order oligomers assembled on tracts of single-strand DNA (ssDNA). Biochemical studies have shown that assembly of recombinase involves accessory factors. These studies have identified a class of proteins, called recombination mediator proteins, that act by promoting assembly of recombinase on ssDNA tracts that are bound by ssDNA-binding protein (ssb). In the absence of mediators, ssb inhibits recombination reactions by competing with recombinase for DNA-binding sites. Here we briefly review mediated recombinase assembly and present results of new in vivo experiments. Immuno-double-staining experiments in Saccharomyces cerevisiae suggest that Rad51, the eukaryotic recombinase, can assemble at or near sites containing ssb (replication protein A, RPA) during the response to DNA damage, consistent with a need for mediator activity. Correspondingly, mediator gene mutants display defects in Rad51 assembly after DNA damage and during meiosis, although the requirements for assembly are distinct in the two cases. In meiosis, both Rad52 and Rad55/57 are required, whereas either Rad52 or Rad55/57 is sufficient to promote assembly of Rad51 in irradiated mitotic cells. Rad52 promotes normal amounts of Rad51 assembly in the absence of Rad55 at 30 degrees C but not 20 degrees C, accounting for the cold sensitivity of rad55 null mutants. Finally, we show that assembly of Rad51 is induced by radiation during S phase but not during G(1), consistent with the role of Rad51 in repairing the spontaneous damage that occurs during DNA replication.

Adenosine Triphosphatases↗
PubMed1998

Role of the acidic carboxyl-terminal domain of the single-stranded DNA-binding protein of bacteriophage T7 in specific protein-protein interactions.

The gene 2.5 single-stranded DNA (ssDNA) binding protein of bacteriophage T7 is essential for T7 DNA replication and recombination. Earlier studies have shown that the COOH-terminal 21 amino acids of the gene 2.5 protein are essential for specific protein-protein interaction with T7 DNA polymerase and T7 DNA helicase/primase. A truncated gene 2.5 protein, in which the acidic COOH-terminal 21 amino acid residues are deleted no longer supports T7 growth, forms dimers, or interacts with either T7 DNA polymerase or T7 helicase/primase in vitro. The single-stranded DNA-binding protein encoded by Escherichia coli (SSB protein) and phage T4 (gene 32 protein) also have acidic COOH-terminal domains, but neither protein can substitute for T7 gene 2.5 protein in vivo. To determine if the specificity for the protein-protein interaction involving gene 2.5 protein resides in its COOH terminus, we replaced the COOH-terminal region of the gene 2.5 protein with the COOH-terminal region from either E. coli SSB protein or T4 gene 32 protein. Both of the two chimeric proteins can substitute for T7 gene 2.5 protein to support the growth of phage T7. The two chimeric proteins, like gene 2.5 protein, form dimers and interact with T7 DNA polymerase and helicase/primase to stimulate their activities. In contrast, chimeric proteins in which the COOH terminus of T7 gene 2.5 protein replaced the COOH terminus of E. coli SSB protein or T4 gene 32 protein cannot support the growth of phage T7. We conclude that an acidic COOH terminus of the gene 2.5 protein is essential for protein-protein interaction, but it alone cannot account for the specificity of the interaction.

Amino Acid Sequence↗
PubMed1999

Replication slippage of different DNA polymerases is inversely related to their strand displacement efficiency.

Replication slippage is a particular type of error caused by DNA polymerases believed to occur both in bacterial and eukaryotic cells. Previous studies have shown that deletion events can occur in Escherichia coli by replication slippage between short duplications and that the main E. coli polymerase, DNA polymerase III holoenzyme is prone to such slippage. In this work, we present evidence that the two other DNA polymerases of E. coli, DNA polymerase I and DNA polymerase II, as well as polymerases of two phages, T4 (T4 pol) and T7 (T7 pol), undergo slippage in vitro, whereas DNA polymerase from another phage, Phi29, does not. Furthermore, we have measured the strand displacement activity of the different polymerases tested for slippage in the absence and in the presence of the E. coli single-stranded DNA-binding protein (SSB), and we show that: (i) polymerases having a strong strand displacement activity cannot slip (DNA polymerase from Phi29); (ii) polymerases devoid of any strand displacement activity slip very efficiently (DNA polymerase II and T4 pol); and (iii) stimulation of the strand displacement activity by E. coli SSB (DNA polymerase I and T7 pol), by phagic SSB (T4 pol), or by a mutation that affects the 3' --> 5' exonuclease domain (DNA polymerase II exo(-) and T7 pol exo(-)) is correlated with the inhibition of slippage. We propose that these observations can be interpreted in terms of a model, for which we have shown that high strand displacement activity of a polymerase diminishes its propensity to slip.

Bacillus Phages↗
PubMed2000

Purification and characterization of DnaC810, a primosomal protein capable of bypassing PriA function.

Escherichia coli strains lacking PriA are severely compromised in their ability to repair UV-damaged DNA and to perform homologous recombination. These phenotypes arise because of a lack of PriA-directed replication fork assembly at recombination intermediates such as D-loops. Naturally arising suppressor mutations in dnaC restore strains carrying the priA2::kan null allele to wild-type function. We have cloned one such gene, dnaC810, and overexpressed, purified, and characterized the DnaC810 protein. DnaC810 can support a PriA-independent synthesis of phiX174 complementary strand DNA. This can be attributed to its ability, unlike wild-type DnaC, to catalyze a SSB-insensitive general priming reaction with DnaB and DnaG on any SSB-coated single-stranded DNA. Gel mobility shift analysis revealed that DnaC810 could load DnaB directly to SSB-coated single-stranded DNA as well as to D loop DNA. This explains the ability of DnaC810 to bypass the requirement for PriA, PriB, PriC, and DnaT during replication fork assembly at recombination intermediates.

Bacterial Proteins↗
PubMed2004

Effect of single-stranded DNA-binding proteins on the helicase and primase activities of the bacteriophage T7 gene 4 protein.

Gene 4 protein (gp4) of bacteriophage T7 provides two essential functions at the T7 replication fork, primase and helicase activities. Previous studies have shown that the single-stranded DNA-binding protein of T7, encoded by gene 2.5, interacts with gp4 and modulates its multiple functions. To further characterize the interactions between gp4 and gene 2.5 protein (gp2.5), we have examined the effect of wild-type and altered gene 2.5 proteins as well as Escherichia coli single-stranded DNA-binding (SSB) protein on the ability of gp4 to synthesize primers, hydrolyze dTTP, and unwind duplex DNA. Wild-type gp2.5 and E. coli SSB protein stimulate primer synthesis and DNA-unwinding activities of gp4 at low concentrations but do not significantly affect single-stranded DNA-dependent hydrolysis of dTTP. Neither protein inhibits the binding of gp4 to single-stranded DNA. The variant gene 2.5 proteins, gp2.5-F232L and gp2.5-Delta26C, inhibit primase, dTTPase, and helicase activities proportional to their increased affinities for DNA. Interestingly, wild-type gp2.5 stimulates the unwinding activity of gp4 except at very high concentrations, whereas E. coli SSB protein is highly inhibitory at relative low concentrations.

Bacteriophage T7↗
PubMed2005

Differential single-stranded DNA binding properties of the paralogous SsbA and SsbB proteins from Streptococcus pneumoniae.

The naturally transformable Gram-positive bacterium Streptococcus pneumoniae has two single-stranded DNA-binding (SSB) proteins, designated SsbA and SsbB. The SsbA protein is similar in size to the well characterized SSB protein from Escherichia coli (SsbEc). The SsbB protein, in contrast, is a smaller protein that is specifically induced during natural transformation and has no counterpart in E. coli. In this report, the single-stranded DNA (ssDNA) binding properties of the SsbA and SsbB proteins were examined and compared with those of the SsbEc protein. The ssDNA binding characteristics of the SsbA protein were similar to those of the SsbEc protein in every ssDNA binding assay used in this study. The SsbB protein differed from the SsbA and SsbEc proteins, however, both in its binding to short homopolymeric dT(n) oligomers (as judged by polyacrylamide gel-shift assays) and in its binding to the longer naturally occurring X and M13 ssDNAs (as judged by agarose gel-shift assays and electron microscopic analysis). The results indicate that an individual SsbB protein binds to ssDNA with an affinity that is similar or higher than that of the SsbA and SsbEc proteins. However, the manner in which multiple SsbB proteins assemble onto a ssDNA molecule differs from that observed with the SsbA and SsbEc proteins. These results represent the first analysis of paralogous SSB proteins from any bacterial species and provide a foundation for further investigations into the biological roles of these proteins.

Amino Acid Sequence↗
PubMed2004

Effect of single and double strap backpacks on lung function.

Carrying heavy and moderate military loads in backpacks or as body armour compresses the chest, causing a change in lung function that is typical of a restrictive ventilatory impairment. It is not known if a lighter backpack load of only 6 kg, such as is typical of loads carried by students, will have a similar effect on lung function. There have been no studies examining whether backpacks of different strapping styles have an effect on lung function. Several designs of student backpack have recently been introduced to the market. One of the most popular is a single-strap backpack. This study examined Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), FEV1.FVC( - 1)% and Peak Expiratory Flow (PEF) in 13 participants (4 males, 9 females) wearing each of two 6 kg backpacks, one with two shoulder straps (a Double Strap Backpack (DSB)) and the other with a single strap (a Single Strap Backpack (SSB)) worn across the shoulder and chest. In comparison with the control of no pack (N), SSB significantly reduced FVC (by 3.94%, p = 0.006) but there were no significant differences in FEV1, FEV1. FVC( - 1)% and PEF. The DSB also significantly reduced FVC (by 1.97%, p = 0.034) but no significant differences were found in FEV1, FEV1. FVC( - 1)% and PEF measures. In comparison with DSB, the SSB was associated with a significantly lower FVC (by 2.05%, p = 0.049) and FEV1 (by 1.88%, p = 0.029) but there were no significant changes in FEV1. FVC( - 1)% and PEF. It is concluded that a backpack load of 6 kg could produce a mild restrictive type of ventilatory impairment in lung function. This effect was greater for a single cross-chest strap than for a more conventional double strap harness.

Adolescent↗
PubMed1996

Evaluation of three methods for the detection of DNA single-strand breaks in human lymphocytes: alkaline elution, nick translation, and single-cell gel electrophoresis.

The aim of this study is to assess the ability of three methods, alkaline elution (AE), nick translation (NT), and single-cell gel electrophoresis (SCGE), to detect DNA single-strand breaks (ssb) in human peripheral blood lymphocytes (HPBL) exposed in vitro to three genotoxic agents; gamma-rays, ethyl methanesulfonate (EMS) and benzo[a]pyrene diol epoxide (BPDE). The ultimate objective is to select the most feasible, sensitive, and reproducible method for the monitoring of populations exposed to genotoxic agents. AE and NT do not seem suitable assays. AE is able to detect DNA lesions induced by the three compounds, but only at relatively high doses (2 Gy, 5 mM EMS and 20 microM BPDE). With NT, DNA alterations induced by gamma-rays are not detected and ssb are only evidenced after exposure to EMS (80 mM), which already alters the viability of the lymphocytes. Nick translation is able to detect ssb induced by 10 microM BPDE. Compared to the other assays, the sensitivity of the SCGE assay is significantly higher since statistically significant changes were detected after incubation with 0.5 mM EMS and 1.25 microM BDPE. SCGE is a relatively simple method, not time-consuming and applicable to a large number of samples per working day. In conclusion, on the basis of the results of this in vitro comparison, SCGE seems a promising method for the monitoring of populations exposed to genotoxic chemicals.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2001

Neuron loss during early adulthood following prenatal low-dose X-irradiation in the mouse brain.

PURPOSE: Apart from subsequent cell death, little is known about long-term effects of a prenatal low-dose X-irradiation (PLDI) on nuclear (n) and mitochondrial (mt) DNA, and whether these effects are connected with reduced neuron numbers in the adult brain. MATERIALS AND METHODS: Pregnant mice were X-irradiated with 0, 10 or 50cGy at day 13 (E13) of pregnancy. One day after (E14), or postnatally at day 25 (P25) or P180, the brains of the offspring were analysed concerning the extent of nDNA repair, mt biogenesis, and the relative content of nDNA single strand breaks (SSB). Stereology was applied for evaluating neuronal loss. RESULTS: One day after irradiation no unrepaired SSB were detected. Significant results were mainly obtained for hippocampal pyramidal cells at P180, particularly cell loss following 50 cGy PLDI, increased SSB content and mt biogenesis (0 vs. 10cGy) but decreased mt biogenesis for 10 vs. 50 cGy. CONCLUSIONS: A hypothesis closely related to that regarding molecular events during aging is presented for explaining this second wave of cell death in adult mice following PLDI as a result of accumulated mtDNA damage caused by PLDI. A possible relation to the neurodegenerative hypothesis of schizophrenia is discussed.

Animals↗
PubMed2002

One-electron oxidation of plasmid DNA by selenium(V) species.

PURPOSE: To employ the gamma-radiation-generated selenium(V) one-electron-oxidizing agent SeO3*- for the preparation of guanyl radicals in plasmid DNA, and to compare the behaviour of this reagent with that of other similarly reactive oxidant species. MATERIALS AND METHODS: Plasmid DNA in aerobic aqueous solution was irradiated with 137Cs gamma-rays (662 keV). The solutions also contained up to 4x10(-2) mol x dm(-3) sodium selenate (Na2SeO4) and/or up to 10(-1) mol x dm(-3) sodium biselenite (NaHSeO3), as well as auxiliary scavengers such as DMSO or glycerol. In some cases, reducing agents such as ferrocyanide were also present. After irradiation, the plasmid was incubated with the Escherichia coli base excision-repair endonuclease formamidopyrimidine-DNA N-glycosylase (FPG). These treatments produced strand breaks in the plasmid. The yields of these strand breaks were quantified by agarose gel electrophoresis. RESULTS: In general, gamma-irradiation produced single-strand breaks (SSB) in plasmid DNA. Subsequent incubation with the endonuclease FPG increased the SSB yield by a factor of 2-100-fold. The smallest effects of FPG were observed when only DMSO or glycerol were present during irradiation. FPG incubation produced significantly larger increases in the SSB yield after gamma-irradiation in the additional presence of selenate and/or biselenite. The largest effect of FPG was observed after gamma-irradiation in the presence of 10(-2) mol x dm(-3) sodium selenate and 10(-1) mol x dm(-3) glycerol. This was indicative of extensive oxidative damage to the plasmid under these conditions and provided evidence for guanine oxidation mediated by SeO3*-. The large effect of FPG was strongly attenuated by the addition of reducing agents such as ferrocyanide. The observations suggest that these reducing agents exert their effects through the reduction of an intermediate guanyl radical. CONCLUSION: By comparing the yields of breaks produced after gamma-irradiation under a range of conditions, it is possible to formulate a reaction scheme that describes the chemical reactions responsible for the formation of strand breaks and FPG-sensitive sites. By applying this scheme to the data, we can quantify rate constants for the reduction of DNA guanyl radicals by reducing agents. This reaction is of particular interest to radiation biology because it is the equivalent of the repair of DNA damage by the direct effect of ionizing radiation.

Binding Sites↗
PubMed2005

Radiation-induced genomic instability in repair deficient mutants of Chinese hamster cells.

PURPOSE: To determine the role of single (SSB) and double strand break (DSB) repair in the induction and propagation of radiation-induced instability. MATERIALS AND METHODS: Two defined hamster cell lines with known DNA repair deficiencies in DSB repair (XR-C1) and base excision repair (EM-C11) and the parental wild-type line (CHO-9) were used. The rate of micronucleus formation, apoptosis and survival were measured at 0, 7 and 14 days after X-ray radiation. RESULTS: An enhanced rate of production of damaged cells was observed in wild type and the repair deficient mutants after irradiation. This was cell type, dose and time-dependent. All cells demonstrated delayed death up to day 14 after irradiation along with an elevated apoptosis frequency. The yield of micronuclei was not significantly increased in the wild-type cells, but was in the mutant cells, over the dose and time range studied. For all three endpoints the increase in damage was most pronounced in the SSB deficient cell line. CONCLUSIONS: SSB and/or oxidized base damage play a major role, rather than DSB, in radiation induced instability.

Animals↗
PubMed2006

Combined electron emission effects on the biologically damaging efficiency of 125I.

PURPOSE: One important obstacle in modeling the biological damage of 125I lies in the collective effects of the emitted electrons. The huge number of possible different ways of atomic rearrangement causes a strong variability in the number and energies of the emitted electrons. The aim of this work is to tabulate, separately for each atomic rearrangement pathway, the absorbed doses and the single-strand breaks (SSB) probabilities for different size nanospheres of liquid water. METHODS: A simple deterministic (non-stochastic) atomic rearrangement model of only 265 pathways is appropriate for modeling the electron-capture and internal conversion processes in 125I. The feasibility of the atomic rearrangement model is verified by comparing the SSB yield for ultrasoft X-ray sources with Lobachevsky's experimental data. RESULTS: A linear equation is sufficient for describing the SSB probability as a function of the dose absorbed in a small volume surrounding the labelled nucleotide 125I-dC. CONCLUSIONS: The application of a deterministic atomic rearrangement model to Auger electron emission spectra gives a new perspective to the study of low linear energy transfer (LET) radiation effects on DNA. The damages induced by point electron-capture (EC) sources and by macroscopic X-ray sources are compared.

DNA↗
PubMed1976

The effect of nitroimidazole and nitroxyl radiosensitizers on the post-irradiation synthesis of DNA.

The modification of DNA damage by three radiosensitizing drugs, present during gamma-irradiation of hypoxic Chinese hamster cells, was investigated. Both 2-methyl-5-nitroimidazole-1-ethanol (metronidazole) and 1-(2-nitro-1-imidazole)-3-methoxy-2-propranol (Ro-07-0582) were found to cause large increases in the yield of DNA single-strand breaks (SSB); triacetoneamine-N-oxyl (TAN) was found to have only a small effect on SSB production. The three drugs tested did not inhibit the rejoining of SSB. A pulse label and chase procedure was used to examine post-irradiation DNA synthesis. TAN present during irradiation under hypoxia was found to cause interruptions in subsequent DNA synthesis. Metronidazole and Ro-07-0582 had no effect on post-irradiation DNA synthesis. In addition, the effects of pre- and post-irradiation exposure to TAN were investigated, since these treatments have shown increased cell-killing in survival studies. TAN pre- and post-treatments were found to have no significant effect on subsequent DNA synthesis.

Cells, Cultured↗
PubMed1977

Effects of daunomycin and radiation on cell-survival and repair of DNA single-strand breaks.

The combined action of Daunomycin and irradiation was investigated using mouse L-929 cells in culture. Survival of cells was measured with the colony assay. Sedimentation in alkaline sucrose gradients was used to study repair of DNA single-strand breaks (SSB) in the presence of various concentrations of Daunomycin. A small increase in radio-sensitivity, as measured by decreasing Do, was obtained for doses of Daunomycin that are considerably toxic to the cells (0.1 microgram/ml). However, the Dq values remained constant even at high concentrations indicating that Daunomycin does not interfere with recovery processes. The rate of rejoining of SSB remained constant up to 1.0 microgram/ml, whereas concentrations of Daunomycin as high as 10 microgram/ml reduced the velocity of repair by a factor of 13. Our data show that concentrations of Daunomycin similar to those required for other DNA-binding drugs are required to inhibit SSB repair. For clinical purposes, no increase in tumour-killing efficiency may be expected from a combined treatment with Daunomycin and radiation.

Animals↗