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PubMed2004

DNA damage and susceptibility to oxidative damage in lymphocytes: effects of carotenoids in vitro and in vivo.

Reports on the effects of carotenoids are conflicting. The present paper examines similarities and differences from contiguous studies in vitro and in vivo. Single-cell gel electrophoresis was used to measure the frequency of single-strand breaks (SSB) in the cell line MOLT-17 (as a model system) and human peripheral blood lymphocytes (PBL). MOLT-17 cells were supplemented with beta-carotene, lutein or lycopene at a range of concentrations (0.00-8.00 micromol/l) using a liposome delivery method. Uptake was dose-dependent. beta-Carotene concentration in the media had no effect on SSB in control cells, but incubation with lycopene or lutein (>2.00 micromol/l) increased the numbers of SSB in control cells. MOLT-17 DNA was less susceptible to oxidative damage (100 micromol H2O2/l, 5 min, 4 degrees C) following incubation with carotenoids between 0.50 and 1.00 micromol/l; at >1.00 micromol/l the effects were ambiguous. Apparently healthy male volunteers supplemented their habitual diets with lutein, beta-carotene or lycopene (natural isolate capsules, 15 mg/d, 4 weeks) in three independent studies, raising plasma concentrations to different extents. Lycopene and lutein had no effect on SSB in control PBL or following oxidative challenge. However, increased plasma beta-carotene was associated with more SSB in control cells whilst PBL DNA resistance to oxidative damage ex vivo was unaffected. These results suggest that the carotenoids are capable of exerting two overlapping but distinct effects: antioxidant protection by scavenging DNA-damaging free radicals and modulation of DNA repair mechanisms.

Adolescent↗
PubMed2000

DNA strand-break yields after post-irradiation incubation with base excision repair endonucleases implicate hydroxyl radical pairs in double-strand break formation.

PURPOSE: To determine the increases in SSB and DSB yields after post gamma-irradiation incubation of plasmid DNA with the Escherichia coli base excision repair endonucleases formamidopyrimidine-DNA N-glycosylase (FPG) and endonuclease III (endo III). MATERIALS AND METHODS: Aqueous solutions of plasmid DNA were irradiated with 137Cs gamma-rays in the presence of 10(-4) - 10(-1) mol dm(-3) formate. After irradiation, aliquots were treated with FPG and/or endo III. SSB and DSB yields were then determined using gel electrophoresis. RESULTS: Both SSB and DSB yields were found to increase after enzyme incubation, with the increase in the DSB yield being approximately equal to the square of the increase in the SSB yield. The correlation between the increases in the SSB and DSB yields was unaffected by the scavenger concentration during irradiation. CONCLUSION: Under the conditions used, the majority of DSB appear to be formed from two hydroxyl radical attacks.

DNA↗
PubMed2003

Difference in the induction, but not in the repair, of X-ray- and nitrogen ion-induced DNA single-strand breaks as measured using human cell extracts.

PURPOSE: To compare the repair efficiency of X-ray (low linear energy transfer [LET]) and nitrogen ion (high LET)-induced single-strand breaks (SSB) in a human cell-free end-joining system. MATERIALS AND METHODS: SSB were introduced into a bacterial plasmid, pBR322, by X-rays (4 MeV photons) and nitrogen ions with an LET=125 keV micro m(-1). Repair efficiency was studied under incubation with the protein extracts from human squamous carcinoma cells, UT-SCC-5. RESULTS: A several fold higher dose of nitrogen ion radiation compared with X-ray radiation was needed to induce a similar loss of supercoiled plasmid DNA. There was no difference in the repair efficiency of SSB induced by these two types of radiation. CONCLUSION: The data indicate that X-rays at 25 Gy and nitroging ions at 100 Gy radiation doses, under condition of low scavenging capacity (10 mM Tris), induce SSB of similar complexity or, alternatively, differences in SSB complexity do not alter the repair rate.

Carcinoma, Squamous Cell↗
PubMed1985

Model studies for the direct effect of high-energy irradiation on DNA. Mechanism of strand break formation induced by laser photoionization of poly U in aqueous solution.

Laser flash photolysis of polyuridylic acid (poly U) in anoxic aqueous solutions leads to biphotonic photoionization of the uracil moiety followed by the formation of single strand breaks (ssb). The rate constant for ssb formation (1.0 s-1, obtained from the slow component of conductivity increase at 23 degrees C and pH 6.8) increases with decreasing pH to 235 s-1 at pH 3.5. The activation energy (pre-exponential factor) was measured to be 66 kJ mol-1 (5 X 10(11) s-1) at pH 6.8. Addition of dithiothreitol (DTT) or glutathione (GSH) prevents ssb formation by reacting with a poly U intermediate (rate constant = 1.2 X 10(6) and 0.16 X 10(6) dm3 mol-1 s-1, respectively). Since with OH radicals as initiators very similar data have been obtained for the kinetics of ssb formation and for the reaction with DTT, we conclude that photoionization of the uracil moiety in poly U leads eventually to the same chemical pathway for ssb formation as that induced by OH radicals. Furthermore, we propose that protection by DTT and GSH occurs via H donation to the C-4' radicals of the sugar moiety of DNA and to the C-4' and the C-2' radicals of poly U.

DNA↗
PubMed1986

Effect of radiomodifying agents on the ratios of X-ray-induced lesions in cellular DNA: use in lethal lesion determination.

The effect of three radiomodifying agents, cysteamine, hyperthermia, and hypoxia, on the induction of the major classes of X-ray-induced DNA lesions, was studied using mouse L cells and Chinese hamster V79 cells. The use of filter elution techniques allowed most of these studies to be conducted at X-ray doses within the survival-curve range. Cysteamine was found to protect against DNA single-strand breakage (ssb), DNA base damage, and DNA-protein crosslinkage. Hyperthermia had no effect on the level of DNA ssb or DNA base damage, but in L cells (but not in V79 cells) it increased the level of DNA-protein crosslinkage relative to DNA ssb. Hypoxia protected against DNA ssb, had no significant effect on the level of DNA base damage, and enhanced the level of DNA-protein crosslinkage relative to DNA ssb. These results support the previous suggestion that the X-ray-induced lethal lesion is DNA double-strand breakage. Implications of these findings for the mechanisms of formation of X-ray-induced DNA lesions are also discussed.

Animals↗
PubMed1989

Repair of DNA single- and double-strand breaks in proliferating and quiescent murine tumor cells.

We evaluated the relationship between the repair of DNA single- and double-strand breaks and cellular radiosensitivity in proliferating vs. quiescent cells of the mouse mammary tumor lines 66 and 67 in vitro, using the technique of filter elution at pH 12.2, pH 7.2 and pH 9.6. In these lines, quiescent (Q; unfed plateau-phase) cells are more radiosensitive than are proliferating (P) cells. At doses of 4-6 Gy, both 66 and 67 Q cells repair single-strand breaks (ssb) with kinetics similar to those of P cells. However, repair of ssb was slightly retarded in Q cells at a higher dose (10 Gy) than at the lower doses. In contrast, repair of ssb in P cells was dose-independent, at least for doses up to 10 Gy. The rate of repair of DNA double-strand breaks (dsb), measured at pH 7.2, was dose-independent in P and Q cells of both lines. The repair kinetics were biphasic, with an initial half-time less than 15 min, and the early phase was similar in all cell groups. The half-time for repair in the slow phase ranged from about 2 to greater than 20 h. The fraction of damage repaired by the slow phase was relatively high in all cell groups (40-70 per cent). In line 66, P cells repaired a higher percentage of dsb by 2 h postirradiation than did Q cells. The opposite was observed in line 67: Q cells repaired more dsb in 2 h than did P cells. The survival of 66 St4 cells (Q cultures which have been refed with complete medium and incubated 4 h) was significantly greater than that of 66 Q; nevertheless St4 cells repaired both ssb and dsb at rates similar to those of Q cells. Therefore, survival does not necessarily correlate with the rates of either ssb or dsb repair among these cell lines in different growth states.

Animals↗
PubMed1993

Sensitivity of neutral filter elution but not PFGE can be modified by non-dsb chromatin damage.

Hamster V79 fibroblast cells and human squamous carcinoma cells (Caski) were exposed to 60Co radiation and DNA double-strand break (dsb) induction was analysed by DNA elution at neutral pH from polycarbonate filter or out of an agarose matrix in pulsed-field electrophoresis (PFGE). While dsb yields were equal for the two cell lines (using 125-iodine calibration) a reduced responsiveness of filter elution was found for V79 versus Caski cells. This difference could be abolished when additional single-strand breaks (ssb) were introduced by an incubation at 10(-4) M H2O2 for up to 40 min that itself did not give a response in neutral elution. No such lack of specificity for the detection of dsb was seen in electrophoretic elution where also the influence of peroxide incubation was absent. The presumed potential of ssb to modify dsb detection was paralleled by the kinetics of dsb rejoining: a pronounced transient increase of DNA elution from filters was observed for V79 cells (less prominent with Caski cells) at 15-40 which is thought to reflect the occurrence of secondary ssb from incisions during base damage repair. Rejoining measured by PFGE did not show this behaviour. The results suggest that ssb may aid decondensation of the chromatin during lysis of cells required for an efficient release of dsb fragments when supported on filters, but which depends on cell type and is less critical in electrophoretic elution out of an agarose matrix. This involvement of ssb in the neutral filter elution assay appears to be contrary to published data obtained with different experimental systems. The finding of an increase of DNA elution from filters due to hyperthermia at 45 degrees C is also taken to indicate an involvement of non-dsb chromatin damage in the response of filter elution at neutral pH with V79 but not with Caski cells.

Animals↗
PubMed1996

Single- and double-strand breaks in pBR322 plasmid DNA by monochromatic X-rays on and off the K-absorption peak of phosphorus.

Using a synchrotron irradiation system pBR322 plasmid DNA was irradiated under vacuum by monochromatic X-rays having five specific photon energies (2.147, 2.153, 2.159, 2.168 and 2.199 keV) both on and off the K-absorption peak (2.153 keV) of phosphorus. The single- and double-strand breaks (ssb and dsb) were measured as conversions of the closed circular form of DNA (form I) to open circular (form II) and linear (form III) forms respectively. Exposures to induce one strand break per molecule were lowest at the peak (2.153 keV), and highest at 2.147 keV; the ratios were 2.7 for ssb and 3.0 for dsb. The exposures for dsb were 21-26 times higher than those for ssb. When the exposures were converted to absorbed doses in grays the absorbed doses per ssb were almost independent of photon energy. This result indicates that a certain absorbed dose was necessary to induce a ssb, regardless of whether photons were absorbed by the K-shell of phosphorus or by other shells, or by other atoms. However, the absorbed dose per dsb at 2.147 keV was 1.17 times higher than that averaged over four X-ray energies above 2-153 keV, indicating that the K-shell absorption, and the subsequent Auger event, efficiently induce dsb. The results are also discussed concerning the number of photo-absorptions of the constituent atoms per DNA strand break.

Animals↗
PubMed1997

The oxygen effect in permeabilized and histone-depleted cells: an enhanced OER for DNA double-strand breaks, compared to single-strand breaks, is abolished by soluble scavengers.

The oxygen enhancement ratios (OER) in mammalian cells for DNA single- and double-strand breaks (ssb and dsb) are similar, usually 2-3. This seems to contradict the hypothesis that dsb are formed by multiple lesions, since one would then expect a quadratic OER for dsb compared to ssb. A higher OER for dsb than for ssb was however found in permeabilized cells (OERdsb = 7.7; OERssb = 4.3) and histone-depleted cells (OERdsb = 20; OERssb = 2.3), in the presence of an SH-compound, mercaptoethylamine. This higher OER could be counteracted by addition of the OH-radical scavenger DMSO. The OERdsb/OERssb ratio thus increases when the indirect effects increase. The repair of directly induced DNA lesions by hydrogen donation seems to be less efficient than the repair of indirectly induced lesions. It is suggested that differences in the fraction of unrepairable breaks differs for ssb and dsb and that this is the reason for the non-quadratic OERdsb compared to OERssb found in cells. In the absence of SH-compounds, there was no oxygen effect for ssb in permeabilized and histone-depleted cells. In contrast to this, a small oxygen effect was observed for dsb in permeabilized cells and this effect increased after histone depletion, reaching a value of OER = 1.8. This oxygen effect seems to be linked to generation of dsb by single OH radicals.

Cell Line↗
PubMed1997

Influence of oxygen on radiation-induced DNA damage in testicular cells of C3H mice.

Radiation-induced DNA single-strand break (ssb) induction and rejoining were measured in murine testicular cells using the alkaline comet assay. Individual cells in different stages of differentiation were identified on the basis of DNA content. As expected, induction of DNA ssb in testis cells irradiated on ice was independent of ploidy, and the extent of damage was similar to that produced in cells from other normal tissues. However, in vivo irradiation of air-breathing mice produced more ssb in haploid than tetraploid germ cells, although their rates of rejoining were similar and comparable to repair rates of cells from other normal tissues. In addition, irradiation of testis in situ produced only half as much damage as irradiation in vitro, and this could be explained only in part by the rapid ssb rejoining occurring during irradiation and cell isolation. A lower cellular oxygenation was postulated to account for the apparent resistance of testis cells to induction of breaks and the difference in induction in relation to DNA content. This was confirmed when carbogen inhalation and treatment with nicotinamide not only increased the overall degree of ssb induction in all these cells, but also reduced differences between cells of different ploidies. Results using the hypoxic cell cytotoxin RSU 1069 confirmed that the extent of hypoxia was not as severe in the testis as in the SCCVII murine tumour. It can be concluded from these data that the oxygenation of all testis cells is low enough to confer radioresistance, and that haploid testis cells are less hypoxic than tetraploid spermatocytes.

Animals↗
PubMed2002

Detection of DNA single-strand breaks and glutathione in mononuclear blood cells of radiotherapy technicians.

We wanted to investigate the effects of gamma radiation on DNA single-strand breaks (SSB) and glutathione (GSH) levels in mononuclear blood cells (MNC) of radiotherapy technicians. DNA SSB in MNC of radiotherapy technicians who use (60)Co-gamma source in their works were detected by alkaline filter elution and compared to control subjects. In addition, GSH levels were measured using the enzymatic method in MNC. Blood samples were collected from radiotherapy technicians on Monday and Friday. DNA SSB levels were found to be significantly higher in smoking controls compared to non-smoking controls. Significant increases of 36% and 49% in DNA SSB were detected from Monday to Friday for non-smoking and smoking radiotherapy technicians, respectively. GSH levels were found to be decreased significantly from Monday to Friday. Gamma-radiation resulted in increased DNA SSB levels of MNC in radiotherapy technicians throughout the working week and these breaks have been observed to be repaired at the weekend. Smoking habit caused an additional increase in the SSBs observed in radiotherapy technicians.

Adult↗
PubMed1992

Modulation by glutathione of DNA strand breaks induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and its aldehyde metabolites in rat hepatocytes.

Activation of the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) produced methylating species and two aldehydes: formaldehyde and 4-oxo-4-(3-pyridyl)-butanal (OPB). We investigated the modulation by glutathione of single-strand breaks (SSB) generated by N-methyl-N-nitrosourea (MNU) and the two aldehydes. Hepatocytes were simultaneously exposed to 0.2 mM MNU and to 0-2.00 mM formaldehyde or OPB for 4 h. Both aldehydes induced SSB in a dose-dependent manner. Formaldehyde and OPB exerted a synergistic effect on the formation of DNA SSB by MNU. It is postulated that both aldehydes interfere with DNA repair processes and thus increase the genotoxic effect of DNA methylating species. We investigated whether glutathione (GSH) could protect DNA from NNK-derived intermediates. Formaldehyde (2 mM) and OPB (2 mM) decreased intracellular GSH contents to 60 and 86% of control respectively. DL-Buthionine-[S,R]-sulfoximine (BSO) treatment reduced the GSH contents of hepatocytes to 19% of control but did not reduce the content of cytochrome P450 nor the metabolism of NNK. The frequency of DNA SSB induced by NNK, formaldehyde or OPB was significantly higher in GSH-depleted hepatocytes. GSH repletion with GSH monoethyl ester returned NNK-induced SSB to its initial frequency. OPB but not NNK nor formaldehyde induced double-strand breaks. We conclude that OPB and formaldehyde inhibit the repair of DNA damage induced by methylating species and that GSH reduces the level of DNA damage induced by NNK-derived reactive metabolites.

Analysis of Variance↗
PubMed1994

DNA single-strand breaks and toxicity induced by 4-(methyl-nitrosamino)-1-(3- pyridyl)-1-butanone or N-nitrosodimethylamine in hamster and rat liver.

Syrian golden hamsters and F344 rats display contrasting susceptibilities to hepatocarcinogenesis induced by the tobacco-specific nitrosamine 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosodimethylamine (NDMA). In this study, the time courses of DNA single-strand breaks (SSB) and toxicity induced by NNK and NDMA in hamster and rat liver were compared. DNA SSB reached a maximum 12 h after carcinogen treatment, partially correlating with previous reports on time courses of DNA methylation. The persistence of DNA SSB up to 2-3 weeks after NNK or NDMA treatment reflects a deficient repair of some DNA lesions. No significant species differences in the kinetics of DNA SSB induction and repair were observed following NNK or NDMA (0.39 mmol/kg) treatment. However, NNK induced slightly more DNA SSB than NDMA in both species. This could reflect the formation of intermediates with more DNA-damaging capacity or inhibiting DNA processes. A significant hepatotoxic effect of NNK, evaluated by plasma markers of liver injury, was observed in rats and hamsters 12-24 h post-treatment. In contrast, NDMA induced earlier (< 12 h) enzyme elevations. Maximum hepatotoxic effects were observed 24 h (NNK-treated hamsters and rats, NDMA-treated rats) or 2 weeks (NDMA-treated hamsters) after carcinogen administration. Three weeks after treatment, hepatotoxicity of NNK and NDMA was still detected in hamsters, but not in rats. These results suggest that the toxic effects of NNK and NDMA initiate a regenerative process that occurs faster in rat than in hamster liver. Since hepatocarcinogenesis occurs in NNK- but not in NDMA-treated rats, promutagenic lesions generated from NNK might be fixed preferentially during cell proliferation.

Alanine Transaminase↗
PubMed1982

DNA repair in human bronchial epithelial cells.

The purpose of this investigation was to compare the response of human cell types (bronchial epithelial cells and fibroblasts and skin fibroblasts) to various DNA damaging agents. Repair of DNA single strand breaks (SSB) induced by 5 krads of X-ray was similar for all cell types; approximately 90% of the DNA SSB were rejoined within one hour. During excision repair of DNA damage from u.v.-radiation, the frequencies of DNA SSB as estimated by the alkaline elution technique, were similar in all cell types. Repair replication as measured by BND cellulose chromatography was also similar in epithelial and fibroblastic cells after u.v.-irradiation. Similar levels of SSB were also observed in epithelial and fibroblastic cells after exposure to chemical carcinogens: 7,12-dimethylbenz[a]anthracene; benzo[a]pyrene diol epoxide (BPDE); or N-methyl-N-nitro-N-nitrosoguanidine. Significant repair replication of BPDE-induced DNA damage was detected in both bronchial epithelial and fibroblastic cells, although the level in fibroblasts was approximately 40% of that in epithelial cells. The pulmonary carcinogen asbestos did not damage DNA. DNA-protein crosslinks induced by formaldehyde were rapidly removed in bronchial cells. Further, epithelial and fibroblastic cells, which were incubated with formaldehyde and the polymerase inhibitor combination of cytosine arabinoside and hydroxyurea, accumulated DNA SSB at approximately equal frequencies. These results should provide a useful background for further investigations of the response of human bronchial cells to various DNA damaging agents.

Asbestos↗
PubMed1984

Single-strand breaks in DNA of various organs of mice induced by methyl methanesulfonate and dimethylsulfoxide determined by the alkaline unwinding technique.

The method for determination of single-strand breaks (SSB) in DNA by the technique of alkaline unwinding and hydroxylapatite chromatography has been applied for cell nuclei from organs of mice. Male mice were given methyl methane-sulfonate (MMS) and dimethylsulfoxide (DMSO) by i.p. administration. Cell nuclei were prepared from various organs and then lysed in alkali. The amount of DNA was determined by fluorometry using 4',6-diamidino-2-phenylindole.2HCl. The relative level of SSB in DNA was determined in various organs (liver, kidney, lung, spleen, testis and brain) 1-24 h after administration of the agent. After MMS-treatment the number of SSB in DNA increased to about the same extent in all organs 1 h post-treatment but then decreased by time. The SSB persisted for the longest time in brain- and lung-DNA. DMSO induced SSB only in DNA of kidney.

Animals↗
PubMed1996

Analysis of DNA alkylation damage and repair in mammalian cells by the comet assay.

The single cell gel electrophoresis (SCGE) or comet assay, which measures DNA strand breaks in individual cells, was used to analyse DNA damage and repair induced by the SN1-type alkylating carcinogens N-ethyl-N'-nitro-N-nitrosoguanidine and N-ethyl-N-nitrosourea in CHO cells. The comet assay was comparable in sensitivity to the alkaline elution assay. The alkyl-adducts detected as DNA single-strand breaks (ssb) by this technique were completely repaired within 24 h after treatment. These data indicate that long-lived lesions, such as alkylphosphotriesters, are not converted into ssb under the standard SCGE alkaline conditions (pH 13.5). The lesions revealed by the comet assay are mainly apurinic/apyrimidinic (AP) sites and breaks formed as intermediates in the base excision repair process of N-alkylpurines. When SCGE was performed at pH 12.5 instead of pH 13.5 a lower level of ssb was detected and these breaks were completely resealed within 2 h after treatment. These data suggest that different subsets of lesions are detected under different pH conditions. The SCGE combined with inclusion within the cells of endonuclease III revealed that a high portion of AP sites induced by alkylation damage were not converted into ssb by alkali. The level of endonuclease III-sensitive sites decreased as a function of the repair time and by 24 h after treatment no sites were left on the DNA. The use of this modified SCGE assay allows the estimation of the total amount of unrepaired AP sites present on DNA. Alkylation-induced ssb as detected by the comet assay should be regarded as an indicator of repair rate and balance more than a measure of actual DNA damage.

Alkylation↗
PubMed1994

Escherichia coli single-stranded DNA binding protein stimulates the DNA deoxyribophosphodiesterase activity of exonuclease I.

The E. coli single-stranded binding protein (SSB) has been demonstrated in vitro to be involved in a number of replicative, DNA renaturation, and protective functions. It was shown previously that SSB can interact with exonuclease I to stimulate the hydrolysis of single-stranded DNA. We demonstrate here that E. coli SSB can also enhance the DNA deoxyribophosphodiesterase (dRpase) activity of exonuclease I by stimulating the release of 2-deoxyribose-5-phosphate from a DNA substrate containing AP endonuclease-incised AP sites, and the release of 4-hydroxy-2-pentenal-5-phosphate from a DNA substrate containing AP lyase-incised AP sites. E. coli SSB and exonuclease I form a protein complex as demonstrated by Superose 12 gel filtration chromatography. These results suggest that SSB may have an important role in the DNA base excision repair pathway.

Bacterial Proteins↗
PubMed1997

Contrasting effects of single stranded DNA binding protein on the activity of uracil DNA glycosylase from Escherichia coli towards different DNA substrates.

Excision of uracil from tetraloop hairpins and single stranded ('unstructured') oligodeoxyribonucleotides by Escherichia coli uracil DNA glycosylase has been investigated. We show that, compared with a single stranded reference substrate, uracil from the first, second, third and the fourth positions of the loops is excised with highly variable efficiencies of 3.21, 0.37, 5.9 and 66.8%, respectively. More importantly, inclusion of E.coli single stranded DNA binding protein (SSB) in the reactions resulted in approximately 7-140-fold increase in the efficiency of uracil excision from the first, second or the third position in the loop but showed no significant effect on its excision from the fourth position. In contrast, the presence of SSB decreased uracil excision from the single stranded ('unstructured') substrates approximately 2-3-fold. The kinetic studies show that the increased efficiency of uracil release from the first, second and the third positions of the tetraloops is due to a combination of both the improved substrate binding and a large increase in the catalytic rates. On the other hand, the decreased efficiency of uracil release from the single stranded substrates ('unstructured') is mostly due to the lowering of the catalytic rates. Chemical probing with KMnO4showed that the presence of SSB resulted in the reduction of cleavage of the nucleotides in the vicinity of dUMP residue in single stranded substrates but their increased susceptibility in the hairpin substrates. We discuss these results to propose that excision of uracil from DNA-SSB complexes by uracil DNA glycosylase involves base flipping. The use of SSB in the various applications of uracil DNA glycosylase is also discussed.

Base Sequence↗