水稻黑条矮缩病毒基因组片段S9的cDNA克隆和全序列分析

应用RT PCR技术克隆了 3个中国水稻黑条矮缩病毒 (riceblack streakeddwarfvirus,RBSDV)分离株基因组片段S9,并测定了它们的全序列。结果表明 :RBSDV浙江分离株 (RBSDV Zj)基因组片段S9全长 190 0nt(EMBL登录号为AJ2 97430 ) ,RBSDV河北分离株 (RBSDV Heb)基因组片段S9全长 1898nt(EMBL登录号为AJ2 9742 9) ,湖北分离株S9全长 190 0nt(EMBL登录号为AJ2 9170 6 )。 3个分离株S9均含有两个开放阅读框(ORF) ,分别编码约 40kD和 2 4kD的多肽。3个中国分离株之间的核苷酸同源性高达 98.5 %～ 98.8% ,与日本分离株S9的核苷酸同源性均为 89.9%～ 90 .2 % ,而与意大利MRDVS8同源性仅为 85 .3%～ 86 .4%。我们发现ORF2十分保守 ,4个RBSDV分离株S9的ORF2同源性高达为 97.6 %～ 10 0 % ,与意大利MRDVS8的ORF2同源性也高达 94.3%。     

慢性蜜蜂麻痹病毒Ch1株的编码区测序及其序列的分析

对中国分离株慢性蜜蜂麻痹病毒(Chronic bee paralysis virus,CBPV)Ch1编码区全基因序列进行克隆、测序、分析。利用RT-PCR方法和生物信息学软件,对本实验室分离到的Ch1株CBPV编码区的基因序列进行克隆,测序,与GenBank收录的CBPV毒株进行同源性比较,并以RdRp为靶基因构建了遗传进化树。结果显示,CBPV Ch1株的编码区由RNA1(GenBank No.KU950353)和RNA2(GenBank No.KU950354)两部分构成,全长5 979个核苷酸。其中RNA1片段全长3 674个核苷酸,编码3个开放阅读框,RNA2片段全长2 305个核苷酸,编码4个开放阅读框,RNA2片段中ORF2和ORF3,可能编码两个结构蛋白,分别命名为SP1和SP2。RNA1和RNA2核苷酸序列与2005年法国分离株Fr2核苷酸序列同源性最高,分别为96.1%和95.5%,但预测蛋白SP1核苷酸序列同源性与2006年乌拉圭分离株Ur1核苷酸序列同源性最高(96.9%)。基于RdRp为靶基因进行了遗传进化分析表明,Ch1株与Fr2株位于同一分支,且在该区域,Ch1株与Fr2株的核苷酸序列同源性最高(96.5%)。本实验成功分离到一株CBPV(KU950353,KU950354),并命名为Ch1株,完成了Ch1株CBPV的编码区的序列测定以及核苷酸序列与推导的氨基酸序列同源性比较及遗传进化分析,为研究CBPV的致病机制和免疫机制提供重要信息。     

马铃薯X病毒湖南分离物的鉴定与分组研究

从湖南石门采集表现重花叶症状的马铃薯叶片中分离纯化到一株线状病毒HN021.经双链RNA(ds-RNA)抽提、寄主反应测定、病毒粒子和内含体的形状观察, 初步确定该病毒为马铃薯X病毒 (Potato virus X).以ds-RNA作为模板,用相应引物对HN021分离物的ORF4-UTR-ORF5片段进行RT-PCR,得到1kb左右的双链cDNA片段.对该片段进行克隆和测序,并将测序所得的核苷酸序列与Genbank登录的11株不同分离物的相应片段的核苷酸序列进行同源性比较和分析.结果表明,HN021与分离自南美洲的三株分离物(COAT,KPA和HB)的同源性为78.4%~79.4%,与其它8株(分离自亚洲、欧洲、大洋州和北美洲)分离物的同源性为96.4%-97.8%.从氨基酸水平比较,HN021与COAT,KPA和HB三者CP和8kDa蛋白氨基酸序列同源性分别为86.5%~89.0%和74.3%~75.7%,相应地与其它8株分离物的同源性分别为97.1%-98.7% 和97.1%-100%.序列分析的结果证实了HN021分离物为马铃薯X病毒,同时表明PVX明显存在两个组(组Ⅰ和组Ⅱ),HN021和其它来自亚洲、欧洲、大洋州、北美洲分离物的组II,3个南美洲分离物属于组I.     

禽Ⅰ型副粘病毒f基因克隆及序列分析

用RT-PCR一步法对云南省不同禽类(鸡、鸽子)3株禽I型副粘病毒F基因进行扩增和克隆,并对其f基因片段核苷酸序列进行分析,结果表明,云南省禽I型副粘病毒各毒株同源性为88.1%～94.9%,与疫苗株LaSota和强毒株F48E9的同源性为85.6%.所分离两株新城疫病毒在F蛋白裂解位点区(112～117aa)的氨基酸序列与强毒株在这一区域的序列完全相同,表明为强毒株.鸽I型副粘病毒F蛋白裂解位点区的氨基酸序列与PPMV ZQ98-1株在这一区域的序列完全相同,揭示为中强毒株.以1 662bp核苷酸绘制系统发育树,表明云南地方新城疫病毒属于基因Ⅶ型,鸽I型副粘病毒属于基因Ⅵ型.     

山羊传染性胸膜肺炎病原体4株国内分离株的重新分类

山羊传染性胸膜肺炎(Contagious Caprine Pleuropneumonia,CCPP)是由山羊支原体山羊肺炎亚种(M.capricolum subsp.capripneumoniae,Mccp)引起的高度接触性传染病,对4株CCPP中国分离株进行分子特征研究,确定其分类地位。针对3段基因(A、B、C),对扩增产物进行酶切鉴定和测序,将结果与丝状支原体簇的6个成员进行遗传衍化分析。在A片段,4株中国分离株的扩增产物经PstI酶切后的结果与Mccp代表株F38相同,为548、420、128等3条带,其他5个丝状支原体簇成员只有420、128bp两条带。在B片段,序列分析结果显示4株中国分离株与F38同源性为99.5%,与山羊支原体山羊亚种Mcc代表株kid的同源性为98.9%,与丝状支原体山羊亚种MmcZZ株同源性仅为95.4%。在C片段研究发现,4株中国分离株的序列与Mmc模式株PG3株同源性为67.4%~67.6%,与2株Mcc8601-50和California Kid同源性为95.1%~98.4%,与3株Mccp97097ET、Gabes和F38的同源性为99.6%~99.8%。通过对中国分离的87001、87002、367、1653等4株CCPP病原体的分子特征研究,首次提出其与山羊支原体山羊肺炎亚种(Mccp)亲缘关系最近,应归属为Mccp,并将国内流行的山羊传染性胸膜肺炎的病原定名为Mccp。     

桃拉综合征病毒中国株ZHZC3全基因测序及分子结构预测

设计8对引物分片段扩增桃拉综合征病毒中国分离株ZHZC3全基因组,病毒两末端序列采用末端快速扩增方法(RACE)获取.扩增产物克隆到pMD18-T载体并测序,用DNAstar软件拼接全序列及同源性比较.结果显示ZHZC3全序列除去3' poly (A)尾,由10202个碱基组成,有两个开放阅读框,分别编码2107和1011个氨基酸的聚蛋白.与美国参考株HI94相比,在编码区没有核苷酸的缺失和插入,但在5' UTR缺失3个A,两者整体核酸同源性达97.9%.ORF1 中ZHZC3与HI94及巴西株(BLZ01)的核酸同源性分别为97.6%、97.7%,在ORF2中ZHZC3与HI94、BLZ01的核酸同源性则分别为98.3、97%.与国外株ORF2的部分序列比较发现ZHZC3和中国台湾株均与美国株HI94同源性最高.克隆分析6株TSV中国大陆株主要结构蛋白CP2基因,发现其编码的氨基酸存在三个高变区,中国大陆株更有其独特的氨基酸变异模式,312 (S), 449 (A), 451 (Q) 和468 (H).表明该病毒的整体变异性不高,但中国的流行株已形成其自己的遗传演变特征.在此基础上,利用生物学软件对CP2蛋白功能域和三维结构进行了预测,为进一步分析CP2蛋白结构与功能关系奠定了基础.ZHZC3株是第一个测定全序列的TSV中国株.     

新疆猪粪便戊型肝炎病毒RNA的检测及序列分析

从戊型肝炎病毒(Hepatitis E virus,HEV)IgG检测阳性的新疆某猪场采集70份猪粪便,利用逆转录套式聚合酶链方法(RT-nPCR),检测HEV RNA,其中13份为阳性,阳性率18.57%.将PCR扩增产物克隆到pMD18-T载体上,构建成重组质粒并测序,结果表明,13株猪源HEV分离株在HEV ORF2 348bp核苷酸序列的同源性为97.1%～100%,为同一基因型;与HEV Ⅰ、Ⅱ、Ⅲ、Ⅳ的同源性分别为74.1%～77.6%,71.6%～74.1%,73.3%～78.2%和82.8%～91.4%,与ⅣA亚型的同源性同源性最高达89.4%～91.4%.以该核苷酸片段绘制的基因进化树显示13株猪源HEV与HEVⅣT1株在同一分支上,属基因Ⅳ型;与国内其他猪源HEV分离株该片段核苷酸序列的同源性为82.6%～91.3%,提示中国猪源HEV的基因型比较一致,同属HEVⅣ型.     

水稻黑条矮缩病毒基因组片段S7的cDNA克隆及全序列分析

应用RTPCR技术克隆了2个水稻黑条矮缩病毒 (rice blackstreaked dwarf virus,RBSDV)中国分离物,即浙江分离物和河北分离物的基因组片段S7,并测定了他们的全序列。结果表明：RBSDV浙江分离物(RBSDVZj)基因组片段S7全长2193nts(EMBL登录号为AJ297427),RBSDV河北分离物基因组片段S7全长2190nts(EMBL登录号为AJ297428),二者均含有两个开放阅读框(open reading frame,ORF),分别编码约41kD和36kD多肽,2个中国分离物核苷酸同源性高达99%,相应的ORF编码的多肽同源性分别为100%和94.4%,与日本RBSDV基因组片段S7核苷酸同源性为93.4%和93.8%,相应ORF编码的多肽同源性分别为98.1%(ORF1)、96.5%和97.8%(ORF2),与意大利MRDV S6核苷酸同源性为85.1%和85.3%,相应多肽同源性分别为92.3%(ORF1)、85.5%和86.8%(ORF2)。     

禽I型副粘病毒f基因克隆及序列分析

用RT-PCR一步法对云南省不同禽类(鸡、鸽子)3株禽I型副粘病毒F基因进行扩增和克隆,并对其f基因片段核苷酸序列进行分析,结果表明,云南省禽I型副粘病毒各毒株同源性为88.1%～94.9%,与疫苗株LaSota和强毒株F48E9的同源性为85.6%。所分离两株新城疫病毒在F蛋白裂解位点区(112～117aa)的氨基酸序列与强毒株在这一区域的序列完全相同,表明为强毒株。鸽I型副粘病毒F蛋白裂解位点区的氨基酸序列与PPMV ZQ98-1株在这一区域的序列完全相同,揭示为中强毒株。以1 662bp核苷酸绘制系统发育树,表明云南地方新城疫病毒属于基因Ⅶ型,鸽I型副粘病毒属于基因Ⅵ型。     

弓形虫上海株的棒状体蛋白ROP2的克隆表达及纯化

根据已发表基因序列(GenBank登录号为Z36906)设计引物,以弓形虫(Toxoplasma gondii)上海本地株的基因组DNA为模板,扩增编码ROP2(rhpotry protein2)蛋白的基因片段,定向克隆至表达质粒pET32a(+),重组质粒经限制性酶切鉴定后测序,结果表明插入片段长度为1044bp,与GenBank上登录的序列相比,同源性为96%-100%,其中与弓形虫RH株的rop2基因同源性为100%。重组原核表达质粒pET32a-rop2转化至大肠杆菌BL21(DE3),经诱导可表达分子量约60.9kD的融合蛋白,能被感染弓形虫RH株的绵羊阳性血清识别。     

Conformational preferences of modified nucleoside N(2)-methylguanosine (m(2)G) and its derivative N(2), N(2)-dimethylguanosine (m(2)(2)G) occur at 26th position (hinge region) in tRNA

Conformational preferences of the modified nucleosides N²-methylguanosine (m²G) and N², N²-dimethylguanosine (m₂²G) have been studied theoretically by using quantum chemical perturbative configuration interaction with localized orbitals (PCILO) method. Automated complete geometry optimization using semiempirical quantum chemical RM1, along with ab initio molecular orbital Hartree–Fock (HF-SCF), and density functional theory (DFT) calculations has also been made to compare the salient features. Single-point energy calculation studies have been made on various models of m²G26:C/A/U44 and m₂²G26:C/A/U44. The glycosyl torsion angle prefers “syn” (χ = 286°) conformation for m²G and m₂²G molecules. These conformations are stabilized by N(3)–HC2′ and N(3)–HC3′ by replacing weak interaction between O5′–HC(8). The N²-methyl substituent of (m²G26) prefers “proximal” or s-trans conformation. It may also prefer “distal” or s-cis conformation that allows base pairing with A/U44 instead of C at the hinge region. Thus, N²-methyl group of m²G may have energetically two stable s-trans m²G:C/A/U or s-cis m²G:A/U rotamers. This could be because of free rotations around C–N bond. Similarly, N², N²-dimethyl substituent of (m₂²G) prefers “distal” conformation that may allow base pairing with A/U instead of C at 44th position. Such orientations of m²G and m₂²G could play an important role in base-stacking interactions at the hinge region of tRNA during protein biosynthesis process.     

Compartment-dependent management of H(2)O(2) by peroxisomes

Peroxisomes (PO) are essential and ubiquitous single-membrane-bound organelles whose ultrastructure is characterized by a matrix and often a crystalloid core. A unique feature is their capacity to generate and degrade H(2)O(2) via several oxidases and catalase, respectively. Handling of H(2)O(2) within PO is poorly understood and, in contrast to mitochondria, they are not regarded as a default H(2)O(2) source. Using an ultrasensitive luminometric H(2)O(2) assay, we show in real time that H(2)O(2) handling by matrix-localized catalase depends on the localization of H(2)O(2) generation in- and outside the PO. Thus, intact PO are inefficient at degrading external but also internal H(2)O(2) that is generated by the core-localized urate oxidase (UOX). Our findings suggest that, in addition to the PO membrane, the matrix forms a significant diffusion barrier for H(2)O(2). In contrast, matrix-generated H(2)O(2) is efficiently degraded. We further show that the tubular structures in crystalloid cores of UOX are associated with and perpendicularly oriented toward the PO membrane. Studies on metabolically active liver slices demonstrate that UOX directly releases H(2)O(2) into the cytoplasm, with the 5-nm primary tubules in crystalloid cores serving as exhaust conduits. Apparently, PO are inefficient detoxifiers of external H(2)O(2) but rather can become an obligatory source of H(2)O(2)--an important signaling molecule and a potential toxin.     

Stereospecific formation of alpha-hydroxycarboxylato oxo peroxo complexes of vanadium(V). Crystal structure of (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O

An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxylatooxoperoxovanadates(V) is presented and the geometric parameters of the V2O2 bridging core are discussed. The first case of a stereospecific formation of oxoperoxovanadates(V) is reported: The crystal structures of the isomeric compounds (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O (lact = C3H4O3(2-), the anion of the lactic acid) differ mainly in the arrangement of the V2O2 core and in mutual orientation of the V=O bonds. The complexes with achiral ligands adopt the same structural type as the complexes formed from a racemic mixture of a chiral ligand, while the structure obtained using an enantiopure L,L-hydroxycarboxylate is different.     

Synthesis and structural characterization of cadmium(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

We have carried out the synthesis of the cadmium coordination compounds [Cd(NO₃)₂(PyTT)(H₂O)] (1) and [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂]_n (2), together with their structural determination by means of X-ray diffraction. The compounds were also characterized through elemental analysis and infrared spectroscopy. The first complex presents a distorted pentagonal bipyramidal geometry with the axial positions occupied by one oxygen atom from a water molecule and a second one from a nitrate ion which acts as a monodentate ligand, whereas the equatorial plane contains three nitrogen atoms from the organic moiety and two oxygen atoms coming from the other nitrate group, which is bidentate. The structure of the second complex consists of parallel sheets linked by van der Waals forces, each one made up of structural units [CdCl₂{(μ-Cl)₂CdCl(μ-Cl)(μ-PyTT)Cd}₂], which possesses two PyTT ligands, 10 bridging chloro ligands and 5 cadmium(II) centres belonging to three environment types: octahedral CdN₂Cl₄, octahedral CdCl₆, on which a centre of symmetry is located, and tetrahedral CdNCl₃, present in a 2:1:2 ratio.     

Molecular-Mechanical studies of the mismatched base analogs of d(CGCGAATTCGCG)2:d(CGTGAATTCGCG)2, d(CGAGAATTCGCG)2, d(CGCGAATTCACG)2, d(CGCGAATTCTCG)2, and d(CGCAGAATTCGCG)·d(CGCGAATTCGCG)

Molecular-mechanical simulations have been carried out on “mismatched base” analogs of the DNA double-helical structure d(CGCGAATTCGCG)₂, in which the base pairs CG at the 3 and 10 positions have been replaced by CA, AG, TC, and TG base pairs, as well as an insertion analog in which an extra adenine has been incorporated into one strand of the above structure between bases 3 and 4. The results of these simulations (calculated relative stabilities, structures, and nmr ring-current shifts) have been compared with calorimetric and nmr data. The calculated relative stabilities of the double-helical parent dodecamer and the various “wobble” base pairs qualitatively correlate with the experimental melting temperatures. The base-pairing structure for the GT wobble pair is in agreement with that previously determined from nmr experiments. For the GA base pair, the structure with both bases anti has a slightly more favorable energy from base pairing and stacking than a structure with non-Watson-Crick H-bonding with adenine syn, in agreement with nmr experiments. The CA wobble base is calculated to favor an adenine 6NH₂ …? cytosine N3 H-bond over cytosine 4NH₂ …? adenine N1, again, in agreement with nmr experiments. There is no definitive experimental data on the TC base pair, but the existence of (somewhat long and weak) H-bonds involving cytosine 4NH₂ …? thymine 4CO and cytosine N3 …? thymine HN3 seems reasonable. We find a structure in which the extra adenine base of the insertion analogs sits “inside” the double helix.     

Effects of CO(2) and O(2) on the Photosynthetic O(2) Evolution of Spirodela polyrrhiza Turions

Net photosynthetic rates of Spirodela polyrrhiza turions, at low O₂ levels, were 6.2 and 38.8 micromoles O₂ per gram fresh weight per hour at 1 millimolar HCO₃⁻ and CO₂ saturation, respectively, and much lower in a regular low-pH growth solution. Air equilibration O₂ concentrations decreased rates considerably, except at CO₂ saturation. The surfacing rate of turions in various inorganic carbon surroundings correlated positively with their photosynthetic rates, but were the same at high and low O₂ levels. The relevance of these findings in relation to environmental conditions conductive to germination of autotrophically growing turions is discussed.     

Conformational analysis of the tetranucleotides m6(2)A-m6(2)A-U-m6(2)A(m6(2)A = N6-dimethyladenosine) and U-m6(2)A-U-m6(2)A and of the hybrid dA-r(U-A). A one- and two-dimensional NMR study

A 1H-NMR investigation was carried out on the tetranucleotides U-m6(2)A-U-m6(2)A and m6(2)A-m6(2)A-U-m6(2)A (m6(2) = N6-dimethyladenosine) as well as on the hybrid trinucleotide dA-r(U-A). An extensive comparison with m6(2)A-U-m6(2)A and other relevant compounds is made. Previous proton NMR studies on trinucleotides have shown that purine-pyrimidine-purine sequences prefer to adopt a mixture of states which have as a common feature that the interior pyrimidine residue bulges out, whereas the flanking purine residues stack upon each other. A stacking interaction on the 3' side of the bulge is known to have no measurable effect on the bulge population. Chemical-shift data, ribose ring conformational analysis and information from NOE experiments now show unambiguously that the moderate U(1)-m6(2)A(2) stack in U-m6(2)A-U-m6(2)A diminishes the population of bulged-out structures in favour of a regular stack. This tendency towards conformational transmission in the downstream 5'----3' direction is fully confirmed by the fact that the strong m6(2)A(1)-m6(2)A(2) stack in the tetranucleotide m6(2)A-m6(2)A-U-m6(2)A virtually precludes the formation of bulged-out structures. The conformational characteristics of dA-r(U-A) appear comparable with those of m6(2)A-U-m6(2)A, which indicates that the presence of a 2'-hydroxyl group in the first purine residue is not a necessary prerequisite for the formation of a bulge.     

Synthesis,spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(3-pyme)2(H2O)2] and polymeric [Cu{3,5-(NO2)2bz}2(3-pyme)2]n

Two new complexes of composition [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] (1) and/or [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂] (2) (3-pyme = 3-pyridylmethanol, ronicol or 3-pyridylcarbinol, 2-NO₂bz = 2-nitrobenzoate and 3,5-(NO₂)₂bz = 3,5-dinitrobenzoate) have been prepared and studied by elemental analysis, electronic, infrared and EPR spectroscopy, magnetic susceptibility measurements and the structure of both complexes has been solved. Complex (1) shows an unusual molecular type of structure consisting of the [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] molecules held together by hydrogen bonds and van der Waals interactions. Complex (2) exhibits a polymeric chain-like structure [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂]_n with copper atoms doubly bridged by two 3-pyridylmethanol molecules and the polymeric molecules are held together by van der Waals interactions. Complex (1) exhibits a magnetic moment μ_eff = 1.84 B.M. at 300 K that remains nearly constant within the temperature region (5–300 K). Further cooling results in lowering the magnetic moment to μ_eff = 1.82 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.423 cm³ K mol⁻¹ and with Weiss constant of −0.06 K. The magnetic moment of (2) exhibits a small increase with a decrease in the temperature (μ_eff = 1.80 B.M. at 300 K and μ_eff = 1.85 B.M. at 1.8 K) with Curie constant of 0.409 cm³ K mol⁻¹ and with Weiss constant of +1.1 K, which can indicate a very weak ferromagnetic interaction between the copper atoms within the chain. Applying the molecular field model resulted in obtaining zJ′ values −0.08 cm⁻¹ for complex (1), and −0.07 cm⁻¹ for complex (2), respectively, that could characterize intermolecular and interchain interactions transmitted through π–π stacking.     

The biological activity of hydrogen peroxide VII. L-Histidine increases incorporation of H(2)O(2) into cells and enhances formation of 8-oxodeoxyguanosine by UV-C plus H(2)O(2) but not by H(2)O(2) alone

L-Histidine (L-His) enhances the clastogenic effects of hydrogen peroxide (H(2)O(2)). We previously suggested the involvement of active transport in the efficient influx of an L-His--H(2)O(2) adduct into cells (Oya-Ohta et al. [1]). In this study, we detected intracellular H(2)O(2) by monitoring formation of 2',7'-dichlorofluorescein (DCF) from its precursor. More fluoroproduct accumulated dose-dependently in cells treated with a mixture of L-His and H(2)O(2) (mixture) than with H(2)O(2) alone. This observation supports our hypothesis that active transport is involved in the enhanced incorporation of H(2)O(2) into cells. Moreover, both mixture and the L-His--H(2)O(2) adduct were less active in the generation of hydroxyl radicals (*OH) upon addition of FeCl(2) than was H(2)O(2) alone in a cell-free system. This result suggests that the Fenton reaction might occur more effectively around the nucleus in cells. An immunohistochemical assay using 8-oxodG-specific monoclonal antibodies did not reveal whether the accumulation of H(2)O(2) generates 8-oxodeoxyguanosine (8-oxodG). No 8-oxodG was evident in cells treated with mixture or with H(2)O(2) alone, or even in cells treated with H(2)O(2) at high doses up to 20 mM and, in some cases, pre-treated with catalase inhibitors. It appears, therefore, that *OH and, specifically, *OH derived from intracellular Fenton reactions, might not play a role in the formation of 8-oxodG. However, exposure to UV-C of cells treated with H(2)O(2) yielded more 8-oxodG in the presence of L-His than in the absence of L-His. Thus, the previously observed enhancing effects of L-His were also noted during the induction of formation of 8-oxodG by UV-C plus H(2)O(2). The formation of 8-oxodG in response to UV-C alone was very limited and, hence, H(2)O(2) seemed to be an effective source of *OH only in the presence of UV-C. It is suggested that the *OH that induces formation of 8-oxodG is not *OH formed via intracellular Fenton reactions but is *OH formed via the dissociation of H(2)O(2) under UV-C.