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Repair of O 6 ‐methyl‐guanine residues in DNA takes place by a similar mechanism in extracts from hela cells, human liver, and rat liver
Author(s) -
Myrnes Bjørnar,
Giercksky Karl Erik,
Krokan Hans
Publication year - 1982
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240200408
Subject(s) - guanine , hela , dna glycosylase , biochemistry , dna , microbiology and biotechnology , cytosine , dna repair , chemistry , biology , cell , gene , nucleotide
Extracts from HeLa S 3 cells, human liver, and rat liver were found to contain an activity that transfers the methyl group from O 6 ‐methyl‐guanine residues in DNA to a cysteine residue of an acceptor protein. The molecular weights of the acceptor proteins in HeLA cells and human liver are 24,000 ± 1,000 and 23,000 ± 1,000. respectively. Assuming that each acceptor molecule is used only once, the average number of acceptor molecules in HeLa cells was calculated to be about 50,000. The extracts also contained 3‐methyl‐adenine‐DNA glycosylase activity and 7‐methyl‐guanine‐DNA glycosylase activity, although the latter activity was not detected in extracts from human liver in our assay system. Thus, the three major alkylation products resulting from the effect of methylating agents, such as N ‐methyl‐ N ‐nitroso urea, can all be repaired in animal cells. Pretreatment of HeLa cells with N ‐methyl‐ N ′‐nitro‐ N ‐nitrosoguanidinc (0.1 μg/ml) strongly reduced the capacity of HeLa cell extracts to repair O 6 ‐methyl‐guanine residues, while the activity of three DNA‐ N ‐glycosylases was essentially unaltered. This inactivation was not caused by a direct methylation of the enzyme by the carcinogen. The results demonstrate that the mechanism of repair of O 6 ‐methyl‐guaninc residues, in DNA is strikingly similar in E coli and animal cells, including humans.