Novel nuclear and mitochondrial glycosylases revealed by disruption of the mouse Nth1 gene encoding an endonuclease III homolog for repair of thymine glycols.
Endonuclease III, encoded by nth in Escherichia coli, removes thymine glycols (Tg), a toxic oxidative DNA lesion. To determine the biological significance of this repair in mammals, we established a mouse model with mutated mNth1, a homolog of nth, by gene targeting. The homozygous mNth1 mutant mice showed no detectable phenotypical abnormality. Embryonic cells with or without wild-type mNth1 showed no difference in sensitivity to menadione or hydrogen peroxide. Tg produced in the mutant mouse liver DNA by X-ray irradiation disappeared with time, though more slowly than in the wild-type mouse. In extracts from mutant mouse liver, we found, instead of mNTH1 activity, at least two novel DNA glycosylase activities against Tg. One activity is significantly higher in the mutant than in wild-type mouse in mitochondria, while the other is another nuclear glycosylase for Tg. These results underscore the importance of base excision repair of Tg both in the nuclei and mitochondria in mammals.
Takao
Masashi
M
Department of Molecular Genetics, Institute of Development, Aging and Cancer, Tohoku University, Sendai 980-8575, Japan.
Kanno
Shin-ichiro
S
Shiromoto
Tatsuya
T
Hasegawa
Rei
R
Ide
Hiroshi
H
Ikeda
Shogo
S
Sarker
Altaf H
AH
Seki
Shuji
S
Xing
James Z
JZ
Le
X Chris
XC
Weinfeld
Michael
M
Kobayashi
Kumiko
K
Miyazaki
Jun-ichi
J
Muijtjens
Manja
M
Hoeijmakers
Jan H J
JH
van der Horst
Gijsbertus
G
Yasui
Akira
A
Sarker
Altraf H
AH
D000483:Alleles; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D004247:DNA / Q000235:genetics / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D004272:DNA, Mitochondrial / Q000235:genetics / Q000528:radiation effects; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000172:deficiency* / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D029968:Escherichia coli Proteins; D005260:Female; D018390:Gene Targeting; D008099:Liver / Q000201:enzymology* / Q000648:ultrastructure; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008930:Mitochondria, Liver / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000302:isolation & purification* / Q000502:physiology; D018384:Oxidative Stress; D010641:Phenotype; D013941:Thymine / Q000031:analogs & derivatives / Q000378:metabolism*
D004272:DNA, Mitochondrial; D029968:Escherichia coli Proteins; D024101:Mitochondrial Proteins; C029389:thymine glycol; D004247:DNA; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; C470703:Nthl1 protein, mouse; D013941:Thymine