type:Journal Article 3. 生物の放射線影響に関する研究（生物系）

type:Journal Article

type:Journal Article

type:Journal Article

type:Journal Article

2011年3月11日に発生した東北地方太平洋沖地震により東日本大震災が引き起こされ、地震と津波により東京電力福島第一原子力発電所事故が起こった。事故により環境に放出された放射性物質が人体に与える影響について懸念された。1986年のチェルノブイリ原子力発電所事故では、放射性ヨウ素の内部被ばくにより、事故後に小児の甲状腺がんの増加が認められたことから、福島県でも子供の健康を長期にわたって見守るため甲状腺検査が開始された。2011年10月より2014年3月までの先行調査が実施され、2014年４月からは本格調査が実施されている。当初の予想に反して、先行検査の段階から多数の甲状腺がんが発見された。この甲状腺がんの増加は、内部被ばくによる発がんではなく、主として超音波検査の質の向上によるものと考えられている。しかしながら、一部が被ばくによる甲状腺がんではないかという考えを否定することは現状では困難であり、今後診断される甲状腺がん症例が内部被ばくよるものか否かを判断する方法も現状ではない。甲状腺がんの発がんのメカニズムの解明や手術適応の確立は、取り組むべき大きな問題であることを認識する必要がある。

Ultraviolet (UV) radiation induces a variety of biological effects, including DNA damage response and cell signaling pathways. We performed transcriptome analysis using microarray in human primary cultured fibroblasts irradiated with UV-C (0.5 or 5 J/m(2)) and harvested at 4 or 12 h following UV exposure. All transcript data were analyzed by comparison with the corresponding results in non-irradiated (control) cells. The number of genes with significantly altered expression (>= 2-fold difference relative to the control) is higher in the sample irradiated with high dose of UV, suggesting that gene expression was UV dose-dependent. Pathway analysis on the upregulated genes at 12 h indicates that the expression of some cell cycle-related genes was predominantly induced irrespective of UV-dose. Interestingly, almost all the genes with significant altered expression were cell cycle-related genes designated as 'Mitotic Genes', which function in the spindle assembly checkpoint. Therefore, even a low dose of UV could affect the transcriptional profile.

Gain-of-function mutations of Saccharomyces cerevisiae pleiotropic drug resistance (PDR) genes PDR1, PDR3, and YRR1 cause constitutive high expression of membrane-associated drug efflux pumps, resulting in the excretion of antifungal drugs. We previously identified a novel mutation of YRR1 that conferred salicylic acid (SA) resistance to S. cerevisiae BY4741 cells randomly mutagenized with ethyl methane sulfonate. Yeast cells carrying the yrr1–52 allele activated several drug efflux pumps and exhibited resistance to 4-nitroquinoline-N-oxide and cycloheximide. However, the activated genes and other factors that are directly involved in SA resistance remain unclear. Therefore, microarray analyses of total RNA extracted from yrr1–52 and wild-type cells during the logarithmic phase were performed. Twenty genes demonstrating > 2-fold higher expression than the wild-type were selected. Among the upregulated genes, YOR1, SNQ2, AZR1, and FLR1 encode transport proteins previously associated with drug efflux pumps. YOR1 and SNQ2, which encode an ATP-binding cassette (ABC) transporter, were investigated as candidate genes involved in SA resistance. Spot assay results showed no changes in SA susceptibility after disruption of YOR1 or SNQ2 on a background of YRR1 and yrr1–52, indicating that Yor1p and Snq2p are not involved in SA resistance.

Yeast cells can extrude intracellular drugs through membrane-associated efflux pumps, such as ATP-binding cassette (ABC) transporters and members of the major facilitator superfamily. Gene expression of drug efflux pumps is regulated by several transcription factors involved in pleiotropic drug resistance (PDR). Salicylic acid (SA) possesses weak antifungal activity. Although the excretion mechanisms of some antifungal drugs have been revealed, the mechanism of SA extrusion remains unclear. To elucidate the mechanism of SA excretion, we screened SA-resistant mutants from random mutagenized Saccharomyces cerevisiae BY4741 cells. We successfully isolated 60 SA-resistant clones (KinSal001-060). KinSal052, one of the strongest SA-resistant clones, also exhibited resistance to 4-nitroquinoline-1-oxide and cycloheximide, indicating that it acquired the PDR phenotype. We identified a novel mutation in YRR1 conferring SA resistance to KinSal052. YRR1 encodes a Zn(II)2Cys6-type zinc-finger transcription factor that reportedly activates gene expression involved in PDR. Yeast cells carrying the yrr1 allele (yrr1-52) activated expression of several efflux pump-encoding genes, including YOR1, SNQ2, AZR1, and FLR1. These results suggested that SA resistance in KinSal052 is conferred by the overexpression of efflux pumps constitutively activated by the mutant form of Yrr1p. © 2013 Elsevier Inc.

[抄録] 糖尿病患者の増加及び高齢化に伴い, 低血糖症例は増加している．重症症例は, 意識障害などのため他者の援助を必要とし, 救急搬送されることが多い．低血糖症例にいかに対応するかは救急医療の現場において重要な問題である．近畿大学医学部附属病院では, 低血糖症例のほとんどが救急診療部門（ER）において初期治療がなされている．当院ERにおいて, 2008年４月から2010年３月までの２年間で84回の低血糖によるER受診があった．意識障害あるいは意識消失を主訴とする症例が多く, 高齢者の割合も高い．内分泌代謝内科で治療されている症例は半数以下であり, 糖尿病以外の疾患のために他の診療科かかりつけとなっている症例が多かった．低血糖症例に対し適切な初期診療を行うために, 当院における低血糖症例の特徴を検討し, 初期診療において必要な情報について解説する．また, 初期診療において, 注意を要する症例として, 低血糖が10時間以上遷延した７症例, 糖尿病治療を受けていなかった非糖尿病の12症例をとりあげる．さらに, 患者の高齢化や社会的な要因から留意すべき点について考察する．

Aim: To evaluate promotive effect of hyperthermia on the carcinostatic activity of synthesized omega-hydroxy fatty acids (ωHFAs) and their ethylesters agaist Ehrlich ascites tumor (EAT) cells. Methods: EAT cells were cultured with either ωHFAs or their ethylester derivatives in a water bath at either 37°C or 42°C for 30 min, followed by incubation in a CO 2 incubator for 20 or 72 h. Mitochondrial dehydrogenase-based WST-1 assay and trypan blue dye exclusion assay were then conducted after incubation. Morphological changes were observed by scanning electron microscopy (SEM). Results: Omega-HFA having a saturated 16-carbon straight-chain (ωH16:0) was the most carcinostatic (at 37°C - viability level: 60.0% at 42°C - 49.6% (WST-1)) among saturated and unsaturated ωHFAs with 12, 15 or 16 carbon atoms, when administrated to EAT cells at 100 μM for 20 h. Carcinostatic activity was markedly enhanced by ethyl-esterization of saturated fatty acids, such as ωH16:0 (at 37°C - 42.3% at 42°C - 11.2% , ibid) and ωH15:0 (at 37°C - 74.6% at 42°C - 25.3% , ibid), and their unsaturated counterparts were extremely effective only in combination with hyperthermia. Prolongation of the incubation period to 72 h at the same concentration increased appreciably their carcinostatic effect (ωH16:0 ethylesther: 1.3% ωH15:0 ethylesther: 8.0%). These values were also supported by dye exclusion assay. The carcinostatic activity enhanced more markedly by hyperthermia (1.2% 2.1%, ibid). SEM shows that ωH16:0 ethylester-exposed EAT cells underwent extensive injury, such as deformation of cell structure or disappearance of microvilli. Conclusions: ωH16:0 ethylester possesses high carcinostatic activity in vitro in combination with hyperthermia and may be utilized as potent anticancer therapeutic agent. Copyright © Experimental Oncology, 2007.

Aim: To evaluate promotive effect of hyperthermia on the carcinostatic activity of synthesized omega-hydroxy fatty acids (ωHFAs) and their ethylesters agaist Ehrlich ascites tumor (EAT) cells. Methods: EAT cells were cultured with either ωHFAs or their ethylester derivatives in a water bath at either 37°C or 42°C for 30 min, followed by incubation in a CO 2 incubator for 20 or 72 h. Mitochondrial dehydrogenase-based WST-1 assay and trypan blue dye exclusion assay were then conducted after incubation. Morphological changes were observed by scanning electron microscopy (SEM). Results: Omega-HFA having a saturated 16-carbon straight-chain (ωH16:0) was the most carcinostatic (at 37°C - viability level: 60.0% at 42°C - 49.6% (WST-1)) among saturated and unsaturated ωHFAs with 12, 15 or 16 carbon atoms, when administrated to EAT cells at 100 μM for 20 h. Carcinostatic activity was markedly enhanced by ethyl-esterization of saturated fatty acids, such as ωH16:0 (at 37°C - 42.3% at 42°C - 11.2% , ibid) and ωH15:0 (at 37°C - 74.6% at 42°C - 25.3% , ibid), and their unsaturated counterparts were extremely effective only in combination with hyperthermia. Prolongation of the incubation period to 72 h at the same concentration increased appreciably their carcinostatic effect (ωH16:0 ethylesther: 1.3% ωH15:0 ethylesther: 8.0%). These values were also supported by dye exclusion assay. The carcinostatic activity enhanced more markedly by hyperthermia (1.2% 2.1%, ibid). SEM shows that ωH16:0 ethylester-exposed EAT cells underwent extensive injury, such as deformation of cell structure or disappearance of microvilli. Conclusions: ωH16:0 ethylester possesses high carcinostatic activity in vitro in combination with hyperthermia and may be utilized as potent anticancer therapeutic agent. Copyright © Experimental Oncology, 2007.

The xeroderma pigmentosum group A protein (XPA) binds to three nucleotide excision repair (NER) factors: RPA, ERCC1, and TFIIH. XPA also binds preferentially to UV- or chemical carcinogen-damaged DNA. In this study, we prepared anti-XPA monoclonal antibodies and examined their effects on NER. Two clones inhibited cell-free NER reactions. The mode of inhibition appeared to differ, one clone inhibited both 5' and 3' incisions equally while the other inhibited the 5' incision more. The two clones inhibited the binding of XPA to RPA, ERCC1, and TFIIH. They did not inhibit the binding to damaged DNA either. These results suggest that the interaction of XPA with these NER factors is essential to the NER pathway. The epitopes of these antibodies were located outside of the binding regions for these NER factors. Steric hindrance or conformational changes of XPA brought about by the binding of anti-XPA IgG possibly cause the inhibitory effects. (C) 2004 Elsevier Inc. All rights reserved.

Damaged DNA bases are removed from mammalian genomes by base excision repair (BER). Single nucleotide BER requires several enzymatic activities, including DNA polymerase and 5',2'-deoxyribose-5-phosphate lyase. Both activities are intrinsic to four human DNA polymerases whose base substitution error rate during gap-filling DNA synthesis varies by more than 10,000-fold. This suggests that BER fidelity could vary over a wide range in an enzyme dependent manner. To investigate this possibility, here we describe an assay to measure the fidelity of BER reactions reconstituted with purified enzymes. When human uracil DNA glycosylase, AP endonuclease, DNA polymerase beta, and DNA ligase 1 replace uracil opposite template A or G, base substitution error rates are less than or equal to0.3 to less than or equal to2.8 x 10(-4). BER error rates are higher when excess incorrect dNTPs are included in the reaction or when wild type DNA polymerase beta is replaced by DNA polymerase beta variants that fill single nucleotide gaps with lower fidelity. Under these conditions, the base substitution fidelity of polymerase beta-dependent BER is 3-8-fold higher than is single nucleotide gap filling by polymerase beta alone. Thus other proteins in the BER reaction may enhance the base substitution fidelity of DNA polymerase beta during single nucleotide BER.

The xeroderma pigmentosum group A protein (XPA) plays a central role in nucleotide excision repair (NER). To identify proteins that bind to XPA, we screened a HeLa cDNA library using the yeast two-hybrid system. Here we report a novel cytoplasmic GTP-binding protein, designated XPA binding protein 1 (XAB1). The deduced amino acid sequence of XAB1 consisted of 374 residues with a molecular weight of 41 kDa and an isoelectric point of 4.65. Sequence analysis revealed that XAB1 has four sequence motifs G1?G4 of the GTP-binding protein family in the N-terminal half. XAB1 also contains an acidic region in the C-terminal portion. Northern blot analysis showed that XAB1 mRNA is expressed ubiquitously, and immunofluorescence analysis revealed that XAB1 is localized mainly in the cytoplasm. Consistent with the GTP-binding motif, purified recombinant XAB1 protein has intrinsic GTPase activity.

We describe here the error specificity of mammalian DNA polymerase eta (pol eta), an enzyme that performs translesion DNA synthesis and may participate in somatic hypermutation of immunoglobulin genes. Both mouse and human pol eta lack intrinsic proofreading exonuclease activity and both copy undamaged DNA inaccurately. Analysis of more than 1500 single-base substitutions by human pol eta indicates that error rates for all 12 mismatches are high and variable depending on the composition and symmetry of the mismatch and its location. pol eta also generates tandem base substitutions at an unprecedented rate, and kinetic analysis indicates that it extends a tandem double mismatch about as efficiently as other replicative enzymes extend single-base mismatches. This ability to use an aberrant primer terminus and the high rate of single and double-base substitutions support the idea that pol eta may forego strict shape complementarity in order to facilitate highly efficient lesion bypass. Relaxed discrimination is further indicated by pol eta infidelity for a wide variety of nucleotide deletion and addition errors. The nature and location of these errors suggest that some may be initiated by strand slippage, while others result from additional mechanisms.

Mutational spectra analysis of 15 immunoglobulin genes suggested that consensus motifs R (G) under bar YW and W (A) under bar were universal descriptors of somatic hypermutation. Highly mutable sites, "hotspots", that matched W (A) under bar were preferentially found in one DNA strand and R (G) under bar YW hotspots were found in both strands, Analysis of base-substitution hotspots in DNA polymerase error spectra showed that 33 of 36 hotspots in the human polymerase eta spectrum conformed to the W (A) under bar consensus. This and four other characteristics of polymerase eta substitution specificity suggest that errors introduced by this enzyme during synthesis of the nontranscribed DNA strand in variable regions may contribute to strand-specific somatic hypermutagenesis of immunoglobulin genes at A-T base pairs.

Human DNA polymerase eta, the product of the skin cancer susceptibility gene XPV, bypasses UV photoproducts in template DNA that block synthesis by other DNA polymerases. Pol eta lacks an intrinsic proofreading exonuclease and copies DNA with low fidelity, such that pol eta errors could contribute to mutagenesis unless they are corrected. Here we provide evidence that pol eta can compete with other human polymerases during replication of duplex DNA, and in so doing it lowers replication fidelity. However, we show that pol eta has low processivity and extends mismatched primer termini less efficiently than matched termini, These properties could provide an opportunity for extrinsic exonuclease(s) to proofread pol eta -induced replication errors. When we tested this hypothesis during replication in human cell extracts, pol eta -induced replication infidelity was found to be modulated by changing the dNTP concentration and to be enhanced by adding dGMP to a replication reaction. Both effects are classical hallmarks of exonucleolytic proofreading. Thus, pol eta is ideally suited for its role in reducing W-induced mutagenesis and skin cancer risk, in that its relaxed base selectivity may facilitate efficient bypass of UV photoproducts, while subsequent proofreading by extrinsic exonuclease(s) may reduce its mutagenic potential.

Mammalian DNA polymerase kappa (pol kappa), a member of the UmuC/DinB nucleotidyl transferase superfamily, has been implicated in spontaneous mutagenesis. Here we show that human pol kappa copies undamaged DNA with average single-base substitution and deletion error rates of 7 x 10(-3) and 2 x 10(-3), respectively. These error rates are high when compared to those of most other DNA polymerases. pol kappa also has unusual error specificity, producing a high proportion of T.CMP mispairs and deleting and adding non-reiterated nucleotides at extraordinary rates. Unlike other members of the UmuC/DinB family, pol kappa can processively synthesize chains of 25 or more nucleotides. This moderate processivity may reflect a contribution of C-terminal residues, which include two zinc clusters. The very low fidelity and moderate processivity of pol kappa is novel in comparison to any previously studied DNA polymerase, and is consistent with a role in spontaneous mutagenesis.

Nucleotide excision repair is a highly versatile DNA repair system responsible for elimination of a wide variety of lesions from the genome. It is comprised of two subpathways: transcription-coupled repair that accomplishes efficient removal of damage blocking transcription and global genome repair. Recently, the basic mechanism of global genome repair has emerged from biochemical studies. However, little is known about transcription-coupled repair in eukaryotes. Here we report the identification of a novel protein designated XAB2 (XPA-binding protein 2) that was identified by virtue of its ability to interact with XPA, a factor central to both nucleotide excision repair subpathways. The XAB2 protein of 855 amino acids consists mainly of 15 tetratricopeptide repeats. In addition to interacting with XPA, immunoprecipitation experiments demonstrafed that a fraction of XAB2 is able to interact with the transcription-coupled repair-specific proteins CSA and CSB as well as RNA polymerase II. Furthermore, antibodies against XAB2 inhibited both transcription-coupled repair and transcription in vivo but not global genome repair when microinjected into living fibroblasts. These results indicate that XAB2 is a novel component involved in transcription-coupled repair and transcription.

A superfamily of DNA polymerases that bypass lesions in DNA has been described(1-4). Some family members are described as error-prone because mutations that inactivate the polymerase reduce damage-induced mutagenesis. In contrast, mutations in the skin cancer susceptibility gene XPV5,6, which encodes DNA polymerase (pol)-eta, lead to increased ultraviolet-induced mutagenesis(7-11). This, and the fact that pol-eta primarily inserts adenines during efficient bypass of thymine-thymine dimers in vitro(8,12,13), has led to the description of pol-eta as error-free. However, here we show that human pol-eta copies undamaged DNA with much lower fidelity than any other template-dependent DNA polymerase studied. Pol-eta lacks an intrinsic proofreading exonuclease activity and, depending on the mismatch, makes one base substitution error for every 18 to 380 nucleotides synthesized. This very low fidelity indicates a relaxed requirement for correct base pairing geometry and indicates that the function of pol-eta may be tightly controlled to prevent potentially mutagenic DNA synthesis.

The XPA (xeroderma pigmentosum group A) protein is a zinc metalloprotein consisting of 273 amino acids which binds preferentially to UV- or chemical carcinogen-damaged DNA, suggesting that it is involved in the recognition of several types of DNA damage during nucleotide excision repair processes. Here we identify a DNA binding domain of the XPA protein, The region of the XPA protein responsible for preferential binding to DNA damaged by UV or cis-diammine-dichloroplatinum(II) (cisplatin) is contained within a truncated derivative of the XPA protein, MF122, consisting of 122 amino acids and containing a C-4 type zinc finger motif, CD (circular dichroism) measurements of the MF122 protein showed that it has a helix-rich secondary structure, suggesting that it is a discretely folded, functional mini-domain. The MF122 protein should be useful for structural investigation of the XPA protein and of its interaction with damaged DNA.

The human XPA and ERCC1 proteins, which are involved in early steps of nucleotide excision repair of DNA, specifically interacted in an in vitro binding assay and a yeast two-hybrid assay. A stretch of consecutive glutamic acid residues in XPA was needed for binding to ERCC1. Binding of XPA to damaged DNA was markedly increased by the interaction of the XPA and ERCC1 proteins. ERCC1 did not enhance binding to DNA when a truncated XPA protein, MF122, was used in place of the XPA protein. MF122 retains damaged DNA binding activity but lacks the region for protein-protein interaction including the E-cluster region. These results suggest that the XPA/ERCC1 interaction may participate in damage-recognition as well as in incision at the 5' site of damage during nucleotide excision repair. (C) 1995 Academic Press. Inc.

XPA is a zinc finger DNA-binding protein, which is missing or altered in group A xeroderma pigmentosum cells and known to be involved in the damage-recognition step of the nucleotide excision repair (NER) processes. Using the yeast two-hybrid system to search for proteins that interact with XPA, we obtained the 34-kDa subunit of replication protein A (RPA, also known as HSSB and RFA). RPA is a stable complex of three polypeptides of 70, 34, 11 kDa and has been shown to be essential in the early steps of NER as well as in replication and recombination. We also demonstrate here that the RPA complex associates with XPA. These results suggest that RPA may cooperate with XPA in the early steps of the NER processes.

We have characterized the human DNA excision repair gene, XPAC (xeroderma pigmentosum group A complementing). This gene of approximately 25 kb consists of six exons. The 5'-flanking region of the gene has a CAAT box, but no TATA box. The region upstream from the coding sequence of exon 1 is G+C rich (73%), and has a GC box. Transcriptional mapping analysis suggested that there is one major transcription start point (tsp). The presence of two polyadenylation signals suggests that the two XPAC mRNAs with different 3' untranslated regions in normal human cells are due to alternative polyadenylations. The promoter activity, measured by transient expression of the cat gene with the 5' flanking regions, indicated the presence of a functional promoter.

代表的な遺伝的早老症としてウェルナー症候群、コケイン症候群、プロジェリアなどがあげられるが、このうちコケイン症候群は、色素性乾皮症、硫黄欠乏性毛髪発育異常症とともにヌクレオチド除去修復機構に異常を持つ。また、色素性乾皮症患者の一部は、進行性の精神神経症状を示し、脳の老化のモデルになることが示唆されている。最近のヌクレオチド除去修復機構の分子機構およびモデルマウスの研究の成果から、コケイン症候群と色素性乾皮症でみられる老化や進行性の神経症状は、転写機構の異常あるいは転写と共役したDNA修復機構の異常と密接な関連があることが明らかになった。

目的：不全心における収縮・拡張不全の原因のひとつとして細胞間接着分子の異常が関係することが明らかになってきた。一方、β受容体遮断薬は心筋症の治療薬として積極的に用いられてきたが作用の詳細は明らかではない、我々は心筋症自然発症動物における接着分子の構造異常に対してβ受容体遮断薬の効果を検討した。 方法：１６週令の心筋症自然発症ハムスターBio14.6（７匹）にβ受容体遮断薬metoprolol (20mg/kg/day) を長期間（２４週間）経口投与し、細胞間接着関連分子（cadherin, vinculin, α-actinin）の構造変化について、心筋組織で間接蛍光抗体法を用いて非投与群（７匹）、正常コントロール群（F1B、７匹）と比較し評価した。心肥大の指標として心重量／体重比、線維化の指標として心筋組織ヒドロキシプロリン量を測定した。 結果：４０週令の非投与群では、心重量／体重比は増加し心肥大が認められた、同様に心筋組織ヒドロキシプロリン量は増加し線維化が進んでいた

Previously, we established 5 kinds of UVB-induced skin cancer cell lines from Xeroderma Pigmentosum A (XPA) deficient mice that has resisitant property against UVC comparing with non-cancerous Xpa-deficient fibroblast. Expression of several mismatch repair (MMR) proteins (Msh2, Msh3, Msh6, Mlh1, Pms2) are reduced in every skin cancer cells. MMR activity is actually down-regulated in addition to dificiency of nucleotide excision repair (NER) activity in the cancer cells. The cancer cells also show abnormal cell cycle profile after UV irradiation different from noncancerous cell.

Background To evaluate whether L-nitroarginine methyl ester (L-NAME), an NO synthase inhibitor, may inhibit beneficial effects of ACEI on cardiac remodeling and function in cardiomyopathic hamsters(Bio14.6) . Methods and Results Bio14.6, received cilazapril (CP )combined with L-NAME from the age of 16 weeks (w). Cardiac hypertrophy (CH) and cardiac fibrosis (CF) treated with CP for 12w or 24w were less than those of the untreated group (n=6, p<0.01). The inhibitory effects of L-NAME on the ACEI-induced recovery in both CH and CF decreased after CP treatment for 24w as compared with 12w . The recovery in fractional shortening by CP was less inhibited with L-NAME in 24w than in 12w. Plasma NOx were higher in 24w than in 12w. CP increased plasma NOx in both stages), and the addition of L-NAME canceled them . Conclusions NO-dependent mechanisms play a major role in ACEI-induced reduction of CH and CF at the early HF stage.

この論文は国立情報学研究所の電子図書館事業により電子化されました。

Damaged DNA bases are removed from mammalian genomes by base excision repair (BER). Single nucleotide BER requires several enzymatic activities, including DNA polymerase and 5',2'-deoxyribose-5-phosphate lyase. Both activities are intrinsic to four human DNA polymerases whose base substitution error rate during gap-filling DNA synthesis varies by more than 10,000-fold. This suggests that BER fidelity could vary over a wide range in an enzyme dependent manner. To investigate this possibility, here we describe an assay to measure the fidelity of BER reactions reconstituted with purified enzymes. When human uracil DNA glycosylase, AP endonuclease, DNA polymerase beta, and DNA ligase 1 replace uracil opposite template A or G, base substitution error rates are

遺伝情報をになうDNAは、様々な外的あるいは内的要因により、絶えず損傷を受けている。紫外線に高感受性を示す色素性乾皮症およびその類縁疾患であるコケイン症候群は、ヌクレオチド除去修復機構(NER)に異常を持つ。NERは、紫外線を始め抗がん剤や発がん物質により作られる損傷を修復する。最近では、DNA修復機構は、転写鎖上のDNA損傷を迅速に修復する転写と共役した修復とゲノム全体の修復との2種類に分けて考えられるようになった。

The Escherichia coli potein DinB is a newly identified DNA polymerase (designated pol IV) with low fidelity and processivity. The efficiency of DNA synthesis by pol IV can be enhanced by the addition of either SSB or β, γ-complex, the processivity components of the pol III holoenzyme. However, it is not known whether the fidelity of pol IV is influenced by such factors. We confirmed that the efficiency of incorporation by pol IV was significantly enhanced by adding SSB and that the processivity was highly increased inthe presence of both SSB and β, γ-complex.

We describe here the error specificity of mammalian DNA polymerase eta (pol eta), an enzyme that performs translesion DNA synthesis and may participate in somatic hypermutation of immunoglobulin genes. Both mouse and human pol eta lack intrinsic proofreading exonuclease activity and both copy undamaged DNA inaccurately. Analysis of more than 1500 single-base substitutions by human pol eta indicates that error rates for all 12 mismatches are high and variable depending on the composition and symmetry of the mismatch and its location. pol eta also generates tandem base substitutions at an unprecedented rate, and kinetic analysis indicates that it extends a tandem double mismatch about as efficiently as other replicative enzymes extend single-base mismatches.