DNA damage repair

The phenomenon that DNA molecules in biological cells recover after being damaged

Collection

zero Useful+1

zero

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Repair of DNA Damage, Biological cell Internal DNA molecule The phenomenon of recovering the structure after being damaged. Research on DNA damage repair helps to understand Gene mutation Mechanism of aging and canceration Can also be applied to the environment Carcinogen Detection of.

In May 2022, the Microbeam Technology and Application Room of the Materials Research Center of the Institute of Modern Physics, Chinese Academy of Sciences made progress in the research of DNA damage repair protein dynamics, and related achievements were published in the Biophysical Journal.^[4]

Chinese name: DNA damage repair
Foreign name: repair of DNA damage
Features: Understand gene mutation mechanism ， be senile Reason for

Application: Detection of environmental carcinogens
Approach: enzyme
test method: Radiology, liquid counting, ultracentrifugation, virus reactivation, dye exchange

catalog

Development History

Announce

edit

DNA damage repair

1949 A Kelner Fortuitous discovery Streptomyces griseus If microorganisms are exposed to visible light immediately after ultraviolet (UV) irradiation, death can be reduced. Since then, this phenomenon has been found in a large number of microbial experiments, and it has been proved that this is the inherent DNA damage repair function of many microorganisms, and this repair function is called Light reactivation 。 1958 R 50. Hill proved that even without visible light Exposure, Escherichia coli It can also repair its DNA damage caused by ultraviolet light, and then prove that other microorganisms also have this function. At that time, this repair function was called dark resurrection or Dark repair 。 Later, it was found that dark repair generally existed in prokaryote , lower eukaryote, higher Eukaryote Of Amphibian Even in mammals, and confirmed that dark repair includes Excision repair and Repair after replication Two. 1968 American scholar J E. Clifford First discovered that Autosome Recessive inheritance Photochemical and cancerous diseases of Xeroderma pigmentosum (XP) is created by Gene mutation Resulting DNA damage excision and repair Caused by functional defects. This discovery is Malignant tumor The occurrence mechanism of molecular biology Evidence also makes the research of DNA damage repair enter the medical field.

Damage type

Announce

edit

DNA molecule There are many types of damage. Two adjacent Thymine (T) Or cytosine (C) covalent bond The ring structure is called cyclobutyryl ring Dimer 。 Thymine dimer The formation of UV is the main damage mode of DNA molecules.

X-ray 、 Gamma ray After irradiation of cells, the free radicals produced by the water inside the cells can make DNA molecules Double chain between hydrogen bond It can also break its single chain or double chain. Bleomycin in chemicals Methanesulfonic acid Methane and other alkylating agents can also cause chain breakage.

Mitomycin C It can cause cross-linking between single strands of DNA molecule, which often occurs in the diagonal of two single strands Guanine between. The cross-linking of chains also often leads to the breaking of DNA molecules.

DNA molecules can also occur individually Base Or nucleotide changes. For example, base structure analogs 5-Bromouracil Can replace individual bases, Nitrite Can cause oxidation of base Deamination reaction ， Protoflavin (Pruhuang), etc acridine Dye like and methyl Aminoazobenzene etc. Aromatic amine Carcinogens can cause individual Nucleotide pair Caused by the increase or decrease of Code shift mutation (See Gene mutation ）。

A DNA damage agent can often cause several types of damage at the same time, and the size and type of its damage effects are related to the dose and the cell cycle state.^[1]

test method

Announce

edit

Most DNA damage repair depends on DNA repair synthesis, so the determination of repair synthesis is often used as DNA repair Test method of. The following are commonly used:

Radiometry

stay cell culture Add in Tritium labelling Of Thymidine etc. Radioactive Source , using Autoradiography Methods The amount of DNA involved in the repair synthesis process was measured by counting the number of silver particles.

Liquid counting method

Full name Liquid scintillation count Determination of trace elements in culture by liquid scintillation counter Radioactive Source The amount involved in DNA molecule due to repair synthesis. This method is suitable for large batch samples.

Ultracentrifugation

A widely used method, which can be applied to Excision repair 、 Repair after replication And the detection of chain fracture repair mode. Generally Tritium labelling bromine deoxidation Uridine Isoparametric DNA molecule To change the weight of DNA molecules（ BrdU Is larger than uracil nucleoside) Ultracentrifugation Can be accessed from Settlement coefficient Collect DNA fragments with different amount of participation in repair synthesis from different components, and then measure them respectively radioactivity To determine the amount of repair synthesis.

Virus reactivation method

with SV40 Viruses adenovirus , herpesvirus, bacteriophage, etc Human cells Or bacteria, and then treated with ultraviolet light to cause virus DNA molecule Because the virus DNA molecule Repair of damage Yes host cell Of Repair enzyme Therefore, whether the damaged virus can survive and reproduce can indirectly reflect the repair function of the host cell.

Dye exchange method

Full name Sister chromatid The detection of sister chromatid exchange rate can also reflect part of DNA repair Function. Some congenital DNA in humans Repair defects Spontaneous SCE was significantly increased in patients with diseases such as Bloom's syndrome; Others such as Xeroderma pigmentosum SCE increased. This is due to the weakening of chromosome stability due to the defect of DNA repair function.

Repair method

Announce

edit

Light reactivation

Also called light reversal. This is visible light (wavelength 3000-6000 A) Photoreactivation enzyme Identify and act on Dimer , using the energy provided by light to open the cyclobutyryl ring to complete the repair process (Figure 2). Photoreactivating enzyme has been used in bacteria, yeast protozoan , algae, frogs, birds, marsupials in mammals, higher mammals and human lymphocyte And skin Fibroblast Found in. Although this repair function is common, it is mainly Lower organism With the evolution of organisms, its role will also be weakened.

Light reactivation The process is not that PR enzyme absorbs visible light, but that PR enzyme first interacts with the Thymine dimer Combine to form a complex, which absorbs visible light in some way, and uses light energy to cut off the C-C bond between thymine dimers. The thymine dimer becomes monomer, and PR enzyme is dissociated from DNA.

Excision repair

also called Cut and repair 。 It was initially found in Escherichia coli, including a series of complex enzymatic DNA repair and replication processes, mainly including the following stages: Endonuclease distinguish DNA damage And make all openings at the 5 'end, and then Exonuclease The damage is removed from 5 'end to 3' end under the action of; Then DNA polymerase Under the action of Complementary chain by Template synthesis New single strand DNA fragments to fill the gaps left after resection; Finally Ligase The newly synthesized single chain segment is connected with the original single chain with phosphodiester chain to complete the repair process (Figure 3).

Excision repair Not limited to repair Pyrimidine dimer It can also repair other types of damage caused by chemicals. From the perspective of the object of excision, excision repair can be divided into Base excision repair and Nucleotide excision repair Two types. Base excision repair is first recognized and removed by glycosylase Base , formed on the single strand of DNA purine Or none pyrimidine The vacant base position can be filled by two ways: one is to use the correct Base insertion To a vacant position; Second, in Endonuclease The DNA strand is cut at the 5 'end of the vacancy under the catalysis of the, thus triggering the above series of excision and repair processes. It is specific for different types of base damage Glycosyl Enzymes are recognized. Different endonucleases also have relative recognition for different types of damage Specificity 。

Excision repair Features are widely available in prokaryote In eukaryotes and eukaryotes, it is also the main repair method for human beings. Rodents (such as hamsters and mice) are congenitally lacking in the function of excision repair.

In 1978, American scholar J.L. Max found that the relationship between eukaryotes and prokaryotes Chromatin The process of excision and repair is different for different structures. Eukaryotic DNA molecule It is not naked like prokaryotes, but entangled in Histone Beaded Nucleosome Structure. Eukaryotic Pyrimidine dimer There are two stages in the resection of DNA: rapid resection, which takes about 2-3 hours, mainly removes the damage of DNA that is not bound to histone; The slow resection period should last at least 35 hours and require some kind of Control factor To identify such damage, expose the damaged part of DNA from the nucleosome, and then complete a series of steps Excision repair Then the repaired DNA molecules are wrapped around histones to form nucleosomes again.

Recombination repair

Recombination repair from DNA molecule Of Semi reserved replication Start at Pyrimidine dimer The corresponding position is vacant due to abnormal replication, which has been confirmed in Escherichia coli DNA damage Induced Recombinant protein , under the action of recombinant protein Mother chain After recombination with the child chain, the gap in the original parent chain can pass through DNA polymerase The function of the opposite subchain is Template synthesis Single strand DNA Pieces to fill, and finally the same Ligase Under the action of Phosphodiester bond Connect the old and new chains to complete the repair process. Recombinant repair is also the main repair method for rodents. Restructuring repair and Excision repair The biggest difference is that the former does not need to remove the damaged part from the parental DNA molecules immediately, but can ensure that DNA replication continues. The damaged part left in the original parent chain can be placed in the next cell cycle And then complete the repair by excision. Recombination repair The main steps of are:

1. Copy

DNA containing TT or other structural damage can still replicate normally, but when it replicates to damage Position, Progeny The newly synthesized strand is shorter than the undamaged strand.

2. Restructuring

complete Mother chain Reconstruct with the child chain with a gap, and the gap is from the parent chain nucleotide Fragment remedy.

3. Re synthesis

After reorganization, the gap in the parent chain passes DNA polymerase To synthesize nucleic acid fragments, and then Ligase Connect the new clip to the old chain, here Recombination repair Done.

The recombination repair did not remove dimers from parental DNA. During the second replication, the dimer left in the parent chain still prevents the replication from proceeding normally, and the cut caused by the replication passing through the damaged part still needs to be made up by the same recombination process. As the DNA replication continues, although the dimer has not been removed for several generations, the damaged DNA chain gradually "dilutes", and finally loses its normal physiological function, The damage will be repaired^[2] 。

SOS repair system

yes SOS reaction A function of. SOS reaction is that DNA is damaged or Deoxyribonucleic acid An induced reaction in which replication is blocked. In E. coli, this reaction is regulated by the recA lex A system. Normally inactive. When there is an inducement signal such as DNA damage Or when replication is blocked to form an exposed single chain, RecA protein Of protease The vitality will be activated and decomposed Repressor LexA protein, related to SOS reaction gene To repress and open successively, producing a series of cellular effects. After the signal causing SOS reaction is eliminated, the protease activity of recA protein is lost, and the lexA protein plays a repressive role again.

When SOS reaction occurs, the damage repair function can be enhanced. For example, uvrA, uvrB, uvrC, uvrD, ssb, recA, recN and ruv genes are developed to enhance Excision repair 、 Repair after replication And chain break repair. And recA and umuD C participates in an unclear mechanism Error prone repair , increase cell survival rate, mutation rate Also increased. In addition to the repair effect, SOS reaction It can also cause cell division to be blocked Lysogenic bacteriophage Release and change of DNA replication form. The latter refers to DNA Polymerase The formation of I * reduces the accuracy of DNA replication and can pass through the damaged site. At this time, the initiation of DNA replication does not require new synthetic proteins.

stay Eukaryotic cell Although the specific process is not clear, there must be inducible error prone repair. Yeast RAD6 system is a kind of error prone repair system. In mammalian cells, DNA damage It can induce the release of virus in cells, virus Transformation Enhancement of chromosome recombination and cell Fibrinolytic enzyme Activator Formation, etc. And we also found that omega, which is similar to E. coli- Reactivation effect And ω - mutagenic effect. Because this reaction can enhance mutation Chromosome rearrangement And virus activity, as well as the impact on DNA replication form, may be related to Oncogene Activation is directly related to tumor formation. Therefore, SOS reaction It can be used as an indicator to detect the carcinogenicity of drugs, and drugs that inhibit SOS reaction can reduce mutation and canceration. This kind of material is called antimutagenic agent.

adaptability

In 1977, American scholar L. Samson and others found that the difference between SOS repair Another kind of Induced reaction , which can be repaired Guanine Base Of Methylation 。 If the culture medium is 1 μ g/ml Mutagen N-Methyl-N '- Nitro － Nitrosoguanidine (MNNG) Cultivating Escherichia coli for two hours can make Escherichia coli resistant to environment with MNNG concentration hundreds of times higher. This is due to the methylation of guanine on the DNA strand induced by MNNG, which induces the synthesis of methyl receptor protein Cysteine It can combine with methyl groups to form S-methylcysteine, so that the methylated guanine base can be repaired.

Chain fracture

include DNA molecule Single chain fracture repair Double chain Fracture repair and chromosome fracture reconnection repair. stay Ligase With the participation of, these fractures can be quickly repaired by reconnection. This repair has two characteristics: first, it is unstable and can be reconnected again dissociation ； Second, it is incorrect. Random reconnection errors often occur.

Chain crosslinking

The initial step is to Glycosyl Enzymes catalyze the uncoupling of a cross-linked arm, and Base The excision method is to repair and synthesize one single chain first, and then Endonuclease Under the catalysis of Nucleotide excision repair The method of repairing the single chain fragment on the opposite side from the opposite direction.^[3]

Practical significance

Announce

edit

tumour

Caused by various reasons DNA damage It can be repaired in various ways. If the repair function is defective, DNA damage may cause two results: one is the cell death ； Second, occurrence Gene mutation Or malignant transformation into tumor cells. Congenital DNA Repair defects Disease patients are prone to various Malignant tumor , such as human Xeroderma pigmentosum The patient's skin is excessively sensitive to the sun, and erythema edema , followed by Pigmentation , dry Hyperkeratosis , as a result Melanoma 、 basal cell carcinoma 、 Squamous cell carcinoma And spinous Epithelioma Occurrence of. adopt cell fusion The study of Genetic heterogeneity , which can be divided into seven parts: A, B, C, D, E, F, G Complementary group And varieties, A-G complementary groups show different degrees of Endonuclease Deficiency induced Excision repair The removal and repair of functional defects and variants are normal, but Repair after replication The function of is defective. Another example Fanconi anemia The main clinical manifestations are as follows Aplastic anemia Growth retardation and susceptibility to leukemia are caused by congenital chain cross-linking Repair defects Caused by. Others such as Bloom's syndrome and Telangiectasia Ataxia Patients are prone to leukemia and Lymphosarcoma It is also caused by congenital defects in DNA repair.

It is worth noting that DNA repair Although functional defect can cause tumor transformed cell Its DNA repair function is not low, on the contrary, it is significantly increased, and can fully repair Chemotherapy drugs DNA caused by damage This is also the reason why most anti-cancer drugs cannot work. Hamster The DNA damage repair of cells is mainly done after replication Plasmacytoma cell Added to the culture of cyclophosphamide etc. Anticancer drug After, Tumor cell Growth as usual, if cyclophosphamide is added at the same time caffeine (Inhibitor of post replication repair), the growth of tumor cells was significantly inhibited. therefore DNA repair The research of combined chemotherapy Provide solutions.

be senile

from DNA repair In the comparative study of function, it was found that animals with long life span (elephant, cattle, etc.) had strong repair function; Short lived animals (hamsters, mice Shrew The repair function is weak. Human DNA repair function is also strong, but it gradually weakens after a certain age, and the number of mutant cells also increases accordingly, so the incidence of cancer in the elderly is relatively high. Detect each age group Normal human chromosome aberration This is confirmed by the DNA repair function and DNA repair rate. Human autosomes Recessive inheritance Of Presenility And Werner's syndrome patients generally die early Cardiovascular disease or Malignant tumor ； The patient's somatic cells are very vulnerable to aging, which is a research Senile disease A good model of the relationship with DNA repair.

immune

DNA repair Patients with congenital functional defects immune system It is also often defective, mainly T lymphocytes Functional defects. With the growth of age, the DNA repair function in cells gradually declines. If it happens at the same time Immune surveillance The functional obstacle will not remove cancerous mutant cells in time, which will lead to the occurrence of tumors. Therefore, aging, DNA repair, immunity and tumor are closely related.

Biochemical test

DNA repair Has been applied to detect various Chemical carcinogen 。 The general method is in vitro Subculture Normal human skin Fibroblast or Rat Primary culture Of Hepatocyte Add the tested substance in the medium, and then add it after a certain period of culture to continue the culture, and then collect the cells for Autoradiography Or liquid scintillation test, if the amount of reference increases significantly, it indicates that the tested object is suspected to be Mutagen Or carcinogen. microbial cultivation The method of Bacillus subtilis Defective recombination function Mutant These mutants cannot be tested because they lose the recombination function Recombination repair Therefore, it is more likely to be killed by many mutagens and carcinogens.

about DNA repair mechanism Many problems in this field need further research and clarification. For example, from prokaryotes to eukaryotes Mammals What are the ways to repair the damaged DNA molecule How does the repair method evolve with the evolution of species, Repair defects What is the essence of genetic heterogeneity of DNA repair What is the causal relationship of functional defects.

Novice on the road

Growth task Getting Started with Editing Edit Rule Edit by myself

I have questions

Content query Online Service Official post bar Feedback

Complaints and suggestions

Report bad information Failed to appeal through entries Complaint of infringement information Blocking query and unblocking

Jinggong Network Anbei No. 1100000200001