Vol. 23-3 Contents
第12 回公開シンポジウム「活性酸素の分子病態学」
12th JEMS Annual Symposium “Molecular Pathogenesis for Oxidative Stress”
酸素ストレスの分子病態学
Molecular pathology of oxidative stress
菊川清見…………………………………………………………………………………………………………………… 137
Kiyomi Kikugawa
活性酸素による突然変異誘発機構－大腸菌の鉄の取り込み調節機構とその活性酸素防御としての役割－
Oxidative mutagenesis― Regulation of iron transporting systems and their role in
protection from oxidative stress in Escherichia coli ―
布柴達男…………………………………………………………………………………………………………………… 147
Tatsuo Nunoshiba
ヒトヌクレオチド除去修復機構によって修復されるDNA酸化損傷とその生物学的意義
Correction of oxygen free-radical induced 5’,8 purine cyclodeoxynucleosides
by the nucleotide excision-repair pathway in human cells
倉岡 功…………………………………………………………………………………………………………………… 159
Isao Kuraoka
哺乳類の酸化損傷塩基修復酵素NTH1とOGG1の基質特異性と作用機序
Substrate specificities and reaction mechanisms of mammalian base excision
repair enzymes NTH1 and OGG1
井出 博…………………………………………………………………………………………………………………… 167
Hiroshi Ide
酸化ストレス発がんの分子機構とその標的遺伝子
Target genes in oxystress-induced carcinogenesis and its molecular mechanisms
豊國伸哉…………………………………………………………………………………………………………………… 177
Shinya Toyokuni
Mechanisms protecting genomic integrity from damage caused by reactive oxygen species：
Implications for carcinogenesis and neurodegeneration
Nakabeppu Y, Tominaga Y, Tsuchimoto D, Ide Y, Hirano S, Sakai Y, Sakumi K and Furuichi M ………… 183
ミトコンドリア遺伝子変異の蓄積と老化
Mitochondrial DNA polymorphisms and aging
田中雅嗣………………………………………………………………………………………………………………………197
Masashi Tanaka
環境因子による酸化的DNA損傷とがん，老化
Mechanism of oxidative DNA damage by environmental chemicals and
its role in carcinogenesis and aging
及川伸二，村田真理子，平工雄介，川西正祐……………………………………………………………………………207
Shinji Oikawa, Mariko Murata, Yusuke Hiraku and Shosuke Kawanishi
一般論文
Original Article
Exposure to a power frequency magnetic field（50 Hz, 40 mT）did not cause point mutation in bacteria
Ikehata M, Takashima Y, Suzuki Y, Shimizu H, Miyakoshi J and Koana T …………………………………… 215
Comparison of mutation spectra induced by ethylating agents in DNA-alkyltransferase-deficient
mutants of E. coli
Ohta T, Hanao K, Tokishita S and Yamagata H …………………………………………………………………… 223
________________________________________
Vol. 23-1 Summary
________________________________________Symposium
酸素ストレスの分子病態学
菊川 清見
東京薬科大学薬学部 〒192-0392 東京都八王子市堀之内1432-1
Molecular pathology of oxidative stress
Kiyomi Kikugawa
School of Pharmacy, Tokyo University of Pharmacy and Life Science
1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
Summary
Intake of molecular oxygen generates oxidative stress in the body.
Oxidative stress induces aging, and results in mutation and several diseases including cancer. This paper
describes aspects of oxidative stress including its generation oxidative damage of biological components
repair and removal of the damage, and also the effect of the damage to the human body.
Furthermore, studies by the authors on the oxidative stress-induced blood cell aging and its modulation
by oxidized protein hydrolase are introduced.
Keywords ： oxidative stress-induced damage, repair and removal system, free radical disease, blood cell
aging, oxidized protein hydrolase
kikugawa@ps.toyaku.ac.jp
受付： 2001 年9 月28 日 受理： 2001 年9 月28 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
活性酸素による突然変異誘発機構
―大腸菌の鉄の取り込み調節機構とその活性酸素防御としての役割―
布柴 達男
東北大学大学院生命科学研究科分子生命科学専攻遺伝子システム学講座
〒980-8578 仙台市青葉区荒巻字青葉
Oxidative mutagenesis
― Regulation of iron transporting systems and their role in
protection from oxidative stress in Escherichia coli ―
Tatsuo Nunoshiba
Department of Biomolecular Science, Graduate School of Life Science, Tohoku University
Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan
Summary
It is generally accepted that iron is one of the most important metals for microorganisms, because it is
essential as a co-factor for a number of enzymes involved in cellular metabolism. However, it is not easily
available to them due to its insolubility in aerobic environments. In order to acquire iron, microorganisms
have evolved iron transport systems wherein so-called siderophores -low molecular weight compounds- are
secreted and which function to chelate iron with high affinity. In addition to the iron transport systems, they
also have a genetic regulation system in which a regulatory protein can sense the cellular level of iron and
controls the gene expression of transport systems. While iron is essential, excess iron is toxic due to its ability
to catalyze Fenton reactions that produce hydroxyl radicals. Thus, these iron-uptake-systems have
important roles in prevention of both iron starvation and oxidative stress. Here we describe the gene regulation
of iron-uptake-systems and their roles in protection from oxidative mutagenesis.
Keywords ： Fur, iron overload, superoxide dismutase, Harber-Weiss/Fenton reaction, mutation spectrum
tnuno@mail.cc.tohoku-ac.jp
受付： 2001 年7 月15 日 受理： 2001 年7 月15 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
ヒトヌクレオチド除去修復機構によって修復される
DNA酸化損傷とその生物学的意義
倉岡 功
大阪大学細胞生体工学センター 〒567-0871 吹田市山田丘1-3
Correction of oxygen free-radical induced 5’,8 purine cyclodeoxynucleosides
by the nucleotide excision-repair pathway in human cells
Isao Kuraoka
Institute of Molecular and Cellular Biology, Osaka University,
1-3 Yamada-oka, Suita, Osaka 565-0871, Japan
Summary
Exposure of cellular DNA to reactive oxygen species generates several classes of base lesions, many of
which are removed by the base excision-repair pathway. However, the lesions include purine cyclodeoxynucleoside
formation by intramolecular cross-linking between the C-8 position of adenine or guanine and the 5’
position of 2-deoxyribose. This distorting form of DNA damage, in which the purine is attached by two covalent
bonds to the sugar-phosphate backbone, occurs as distinct diastereoisomers（R and S）. It was
observed here that both diastereoisomers block primer extension by mammalian and microbial replicative
DNA polymerases, using DNA with a site-specific purine cyclodeoxynucleoside residue as template, and
consequently appear to be cytotoxic lesions. The two forms of purine cyclodeoxynucleoside also interfered
with digestion by 3’-5’ exonuclease. Plasmid DNA containing either the 5’R or 5’S form of 5’,8 cyclo-2-
deoxyadenosine was a substrate for the human nucleotide excision-repair enzyme complex. The R isomer
was more efficiently repaired than the S isomer. No correction of the lesion by direct damage reversal or
base excision-repair was detected. Dual incision around the lesion was dependent on the core nucleotide
excision-repair protein XPA. In contrast to several other types of oxidative DNA damage, purine
cyclodeoxynucleosides are chemically stable and would be expected to accumulate at a slow rate over many
years in the DNA of non-regenerating cells from xeroderma pigmentosum patients. High levels of this form
of DNA damage may help explain the progressive neurodegeneration seen in XPA individuals.
Keywords ： cyclopurine deoxynucleosides, nucleotide excision repair, xeroderma pigmentosum, neurodegeneration
ikuraoka@imcb.osaka-u.ac.jp
受付： 2001 年9 月18 日 受理： 2001 年9 月18 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
哺乳類の酸化損傷塩基修復酵素NTH1とOGG1の
基質特異性と作用機序
井出 博
広島大学大学院理学研究科数理分子生命理学専攻
〒739-8526 東広島市鏡山1-3-1
Substrate specificities and reaction mechanisms of mammalian base excision
repair enzymes NTH1 and OGG1
Hiroshi Ide
Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University,
Higashi-Hiroshima 739-8526, Japan
Summary
Reactive oxygen species generate structurally diverse base lesions in DNA. In E. coli cells, oxidative
pyrimidine lesions are removed by Endo III and Endo VIII, whereas oxidative purine lesions by Fpg. In the
present study, substrate specificities and reaction mechanisms of NTH1, a mammalian homologue of Endo
III, and OGG1, a mammalian functional homologue of Fpg, were characterized using defined oligonucleotide
substrates and the obtained results were compared to those of Endo III and Fpg. Mouse NTH1（mNTH1）
recognized not only urea（UR）, thymine glycol（TG）, 5,6-dihydrothymine（DHT）, and 5-hydroxyuracil
（HOU）derived from pyrimidine bases but also formamidopyrimidine（FAPY）derived from guanine. With
both mNTH1 and human NTH1, the activity for FAPY was comparable to TG. Unlike Endo III, the activities
of mNTH1 for these lesions were essentially independent of paired bases. Human OGG1（hOGG1）recognized
7, 8-dihydro-8-oxoguanine（OG）and FAPY. hOGG1 excised OG in a paired base-dependent manner
but paired base effects were not evident for FAPY. The difference in the activity for the most preferred
OG： C and the least preferred OG ： A was 20-fold, while that for the most preferred FAPY ： C and the
least preferred FAPY ： A was only 2.3-fold. These results indicate that FAPY ： C is a good substrate for
both NTH1 and OGG1, suggesting participation of the two enzymes in repair of this lesion in mammalian
cells. In contrast, Endo III and Endo VIII recognized FAPY ： C very poorly relative to TG. Determination of
enzymatic parameters revealed that catalytic rate constants（kcat）of mNTH1 and hOGG1 were much lower
than those of Endo III and Fpg. It seems that distinctive rate determining steps for the enzymatic reaction
are responsible for the differential paired base effects observed for Endo III and mNTH1. For Endo III with
high kcat, the rate determining step is flip out of a damaged base, thereby making the activity sensitive to
paired bases. In contrast, for mNTH1 with low kcat, the rate determining step is subsequent N-glycosylase
and/or AP lyase, thereby making the activity insensitive to paired bases.
Keywords ： oxidative base damage, NTH1, OGG1, substrate specificity, paired base effects
ideh@hiroshima-u.ac.jp
受付： 2001 年9 月27 日 受理： 2001 年9 月27 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
酸化ストレス発がんの分子機構とその標的遺伝子
豊國 伸哉
京都大学大学院医学研究科基礎病態学講座病態生物医学専攻
〒606-8501 京都市左京区吉田近衛町
Target genes in oxystress-induced carcinogenesis and its molecular mechanisms
Shinya Toyokuni
Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University
Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
Summary
Oxidative stress has been associated with carcinogenesis. In 1982, our laboratory established an oxystress-
induced carcinogenesis model of rodent kidney by the use of an iron chelate, ferric nitrilotriacetate.
This model is unique in that 1）only carcinoma, not sarcoma, is induced, 2）the induced tumor is of high
malignant potential to kill the animal by pulmonary metastasis, peritoneal invasion or rupture of the primary
tumor, and, 3）increase in a variety of covalently modified products including 8-oxoguanine, thymine-tyrosine
cross-link, 4-hydroxy-2-nonenal and its modified proteins are demonstrated in its early stage. Since in
general free radicals are not considered to react with specific target molecules in contrast with immune reaction,
we undertook to answer the question whether there is any specific target gene（s）in this carcinogenesis
model. By genetically analyzing F1 hybrid rats, we found two chromosomal areas that showed a high
incidence of loss of heterozygosity, which lead to a finding that p15INK4B/p16INK4A tumor suppressor genes
are one of the major pathways responsible for this oxystress-induced cancer. Furthermore, by screening
84,000 transcripts by differential display techniques, we found that at least 15 genes associated with stressresponse
or cellular proliferation are differentially expressed in this model. We believe that not only genetic
changes but also epigenetic changes play a role in oxidative stress-induced carcinogenesis.
Keywords ： oxidative stress, iron, carcinogenesis, allelic loss, p16 tumor suppressor gene
toyokuni@path1.med.kyoto-u.ac.jp
受付： 2001 年9 月6 日 受理： 2001 年9 月6 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
Mechanisms protecting genomic integrity from damage caused
by reactive oxygen species: Implications for carcinogenesis
and neurodegeneration
Yusaku Nakabeppu*, Yohei Tominaga, Daisuke Tsuchimoto, Yasuhito Ide,
Seiki Hirano, Yasunari Sakai, Kunihiko Sakumi and Masato Furuichi
Division of Neurofunctional Genomics, Medical Institute of Bioregulation, Kyushu University,
and CREST, JST, 3-1-1 Maidashi, Higashi-Ku, Fukuoka 812-8582, Japan
Summary
In mammalian cells, more than one genome in a single cell has to be maintained throughout the
entire life of the cell, one in the nucleus and the other in the mitochondria. It seems likely that the
genomes and their precursor nucleotides are highly exposed to reactive oxygen species, which are
inevitably generated as a result of the respiratory function in mitochondria. To counteract such
oxidative damage in nucleic acids, these cells are equipped with several defense mechanisms.
Modified nucleotides in the nucleotide pools are hydrolyzed, thus avoiding their incorporation during
synthesis of DNA or RNA. Damaged bases in DNA with relatively small chemical alterations,
are mainly repaired by the base excision repair (BER) system, which is initiated by the excision of
damaged bases by specific DNA glycosylases. Human MTH1 (hMTH1) protein hydrolyzes oxidized
purine nucleoside triphosphates, such as 8-oxo-dGTP, 8-oxo-dATP and 2-hydroxy (OH)-dATP
to the monophosphates. In human cells, multi-forms of hMTH1 polypeptides are located in the
cytoplasm, mitochondria and nucleus, and their synthesis is regulated by both alternative splicing of
the transcripts and the alternative initiation of their translation, both of which are further altered by
a single nucleotide polymorphism. We observed an increased susceptibility to spontaneous carcinogenesis
in mth1 deficient mice, and alteration of MTH1 expression along with accumulation of 8-
oxo-dG in patients with various neurodegenerative diseases. Human enzymes for the BER pathway,
namely 8-oxoG DNA glycosylase (hOGG1), 2-OH-A/adenine DNA glycosylase (hMYH), and a novel
AP endonuclease (hAPE2) are also located in the mitochondria as well as the nuclei in human cells,
and the expression of mitochondrial OGG1 is altered in patients with various neurodegenerative diseases.
Furthermore, MYH and APE2 have a functional PCNA binding motif, thus suggesting that
the PCNA-dependent post-replicative BER plays an essential role in the repair of such misincorporated
bases as 2-OH-dA or adenine opposite 8-oxoG in templates.
Keywords: oxidative damage, DNA repair, mutation, cell death, mitochondria
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
＊ yusaku@bioreg.kyushu-u.ac.jp
Received: October 2, 2001, accepted: October 2, 2001
Environmental Mutagen Society of Japan
ミトコンドリア遺伝子変異の蓄積と老化
田中 雅嗣
岐阜県国際バイオ研究所遺伝子治療研究部 〒505-0116 岐阜県可児郡御嵩町八木記念パーク
Mitochondrial DNA polymorphisms and aging
Masashi Tanaka
Gifu International Institute of Biotechnology
Summary
All of the genes in mitochondrial DNA（mtDNA）are fully expressed in cells, whereas only 1.5 ％ of the
nuclear DNA（nDNA）is functionally expressed. Assuming that the copy number of mtDNA is 2000 per
cell, the total functioning mtDNA is 3 × 107 bp, which is 1/3 of the functioning nDNA. Because the evolutionary
rate of mtDNA is 5-10 times higher than that of nDNA, the functional significance of the single
nucleotide polymorphisms（SNPs）in mtDNA is comparable to those in nDNA. Thus, SNPs in mtDNA are
expected to influence the susceptibility of individuals to various diseases in combination with SNPs in
nDNA.
First, we analyzed synonymous mutations in mtDNA to understand the mutational mechanisms.
Replication of mtDNA is highly asymmetric between the heavy（H）and light（L）strands. The parental H
strand is displaced by the daughter H strand and remains in a single-stranded state until the daughter L
strand is synthesized. Occurrence of nucleotide substitutions was distinctly asymmetric between the two
strands ；G→ A and T → C transitions were 9-fold and 1.8-fold more frequent on the L strand than on the H
strand, respectively. This nucleotide substitution bias is consistent with the T- and G-abundance of the H
strand as well as the A- and C-abundance of the L strand. Deamination of cytosine to uracil or adenine to
hypoxanthine in the single-stranded state of the parental H strand seems to contribute to the mutagenesis in
mtDNA.
Second, we examined the effect of mitochondrial genotypes on the predisposition to longevity or various
diseases. Mt5178A, causing a Leu → Met replacement in the ND2 gene, was more frequently observed in
centenarians than in controls. The longevity-associated genotype Mt5178A predisposes resistance to adultonset
diseases. We have confirmed that Mt5178A exhibits an anti-arteriosclerotic effect at least in diabetic
patients. Genotyping of patients with mitochondrial diseases has revealed that the Mt5178A genotype suppresses
the occurrence of mtDNA mutations, especially the Mt8993 T→ G transversion. Because T →G
transversion can be induced by oxidative damage to DNA, the difference in the occurrence of this mutation
may be relevant to the functional differences between genotypes Mt5178A and Mt5178C. We can also speculate
that the rates of age-associated accumulation of mitochondrial mutations in somatic cells are different
between these mitochondrial genotypes.
Keywords ： mitochondrial DNA, deamination, uracil, hypoxanthine, longevity
mtanaka@giib.or.jp
受付： 2001 年11 月17 日 受理： 2001 年11 月17 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
環境因子による酸化的DNA損傷とがん，老化
及川 伸二，村田 真理子，平工 雄介，川西 正祐＊
三重大学医学部衛生学教室 〒514-8507 三重県津市江戸橋2 丁目174
Mechanism of oxidative DNA damage by environmental chemicals and
its role in carcinogenesis and aging
Shinji Oikawa, Mariko Murata, Yusuke Hiraku and Shosuke Kawanishi
Department of Hygiene, Mie University School of Medicine, 2-174 Edobashi, Tsu, Mie, 514-8507, Japan
Summary
Reactive oxygen species are capable of causing damage to various cellular constituents, such as DNA, proteins
and lipids, leading to carcinogenesis, aging and a number of diseases. We have investigated the
sequence specificity of oxidative stress-mediated DNA damage by using 32P-labeled DNA fragments
obtained from the human c-Ha-ras-1, p53 and p16 genes. The sequence specificity of DNA damage plays the
key role in the mutagenic process, and affects the mutation frequency. Therefore, investigation on sequence
specificity of DNA damage would provide clues on the biological significance of DNA damage which in turn
may be beneficial for cancer prevention strategy. Here we discuss the mechanisms and sequence specificity
of DNA damage caused by various environmental chemicals and UVA-activated photosensitizers in relation
to carcinogenesis and aging.
Keywords ： DNA damage, carcinogenesis, aging, environmental chemicals, reactive oxygen species
＊ kawanisi@doc.medic.mie-u.ac.jp
受付： 2001 年11 月12 日 受理： 2001 年11 月12 日
･日本環境変異原学会
本稿は日本環境変異原学会第12 回公開シンポジウム「活性酸素の分子病態学」で発表された．
This paper was presented at the 12th JEMS Annual Symposium at the Nagai Memorial Hall, Tokyo, May 26th, 2001. The symposium entitled
“Molecular Pathogenesis for Oxidative Stress”, was organized by Tatsuo Nunoshiba and sponsored by the Japanese Environmental Mutagen
Society.
________________________________________Original Article
Exposure to a power frequency magnetic field (50 Hz, 40 mT)
did not cause point mutation in bacteria
Masateru Ikehata1*, Yoshio Takashima2, Yuji Suzuki3, Hidesuke Shimizu3,
Junji Miyakoshi4 and Takao Koana1,2
1 Biotechnology Laboratory, Railway Technical Research Institute, 2-8-38, Hikari-cho,
Kokubunji, Tokyo 185-8540, Japan
2 Department of Built Environment, Tokyo Institute of Technology, 4259 Nagatsuta-cho,
Midori-ku, Yokohama, Kanagawa 226-8502, Japan
3 Department of Public Health and Environmental Medicine, Jikei University School of
Medicine, 3-25-8, Nishishinbashi, Minato-ku, Tokyo 105-8461, Japan
4 Department of Radiation Genetics, Graduate School of Medicine, Kyoto University,
Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
Summary
Possible mutagenic effects of 50 Hz sinusoidal magnetic fields (MFs) were estimated using bacterial
mutation assay. Mutagenic potential of MFs of up to 40 mTesla (1 T = 10,000 Gauss) was not
detected by the bacterial mutation assay using Escherichia coli WP2 uvrA and four strains of
Salmonella typhimurium (TA98, TA100, TA1535, TA1537), either in the pre-incubation method or in
the plate incorporation method. This suggested that 50 Hz, up to 40 mT MFs does not cause base
substitutions or frame-shifts in bacteria.
Keywords: magnetic fields, extremely low frequency, Ames test, mutagenesis
* ikehata@rtri.or.jp
Received: March 16, 2001, accepted: August 13, 2001
Environmental Mutagen Society of Japanﾊ
Comparison of mutation spectra induced by ethylating agents
in DNA-alkyltransferase-deficient mutants of E. coli
Toshihiro Ohta*, Kouhei Hanao, Shin-ichi Tokishita and Hideo Yamagata
School of Life Science, Tokyo University of Pharmacy and Life Science
1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
Summary
The mutational spectra of ethylating agents, N-ethyl-N’-nitro-N-nitrosoguanidine (ENNG) and Nethyl-
N-nitrosourea (ENU), were investigated using lacZ reversion assay in Escherichia coli ada and
ogt mutants. ENNG and ENU induced all types of base substitutions with G : C→A : T transitions
most predominant, followed by A : T→G : C transitions. In an ada background, induction of G : C→
A : T and A : T→G : C transitions were not enhanced, while 4 types of transversions (G : C→T : A,
A : T→C : G, G : C→C : G, and A : T→T : A) were induced more strongly than in a wild-type background.
In an ogt background, however, the opposite effects were observed, i.e. ENNG and ENU
induced considerable increase of G : C→A : T and A : T→G : C transitions while no difference in
transversions was observed between ogt mutant and its parent strain.
Keywords: mutation spectrum, ENNG, ENU, ada, ogt
* ohta@ls.toyaku.ac.jp
Received: April 17, 2001, accepted: June 13, 2001
Environmental Mutagen Society of Japan