Characterization of O6-methylguanine-DNA methyltransferase in transgenic mice introduced with the E. coli ada gene.
The characteristics of O6-methylguanine-DNA methyltransferase (O6-MTase) produced in transgenic mice, in which the introduced E. coli ada gene was expressed under the control of the metallothionein promoter, were investigated. Liver extracts from transgenic homozygotes showed approximately 3 times the control activity, a marked increase of up to about 8 times the non-transgenic control levels being observed 10 h after zinc treatment. Examination of the substrate specificity of the enzyme revealed that the activity in the transgenic mice is due to the introduced foreign gene. The enzyme possessed methylphosphotriester-DNA methyltransferase as well as O6-MTase, characteristic of the E. coli Ada protein. Comparison of differences in biological response between transgenic and non-transgenic mice after treatment with the alkylating carcinogen methylnitrosourea (MNU) at various doses revealed transgenic mice to be more capable of repairing O6-MTase activity, only showing signs of exhaustion at very high levels of exposure. In non-transgenic mice, on the other hand, the basal level of O6-MTase was low, and the activity was hardly detectable when the animals were treated with MNU.
Nakatsuru
Y
Y
Department of Experimental Pathology, Cancer Institute, Tokyo, Japan.
Matsukuma
S
S
Sekiguchi
M
M
Ishikawa
T
T
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005260:Female; D005798:Genes, Bacterial; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008770:Methylnitrosourea / Q000494:pharmacology; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D008822:Mice, Transgenic / Q000235:genetics*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D014157:Transcription Factors
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D014157:Transcription Factors; D008770:Methylnitrosourea; D008780:Methyltransferases; C045675:Ada protein, E coli; D019853:O(6)-Methylguanine-DNA Methyltransferase