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The DNA repair enzyme O6-methylguanine-DNA methyltransferase has been used as a reagent to analyse the initial reaction sites of alkylating agents such as chloroethylnitrosourea that cross-link DNA. The transferase can be employed for this purpose because it removes substituted ethyl groups from DNA, as shown by its ability to act on O6-hydroxyethylguanine residues in DNA. The enzyme counteracts the formation of interstrand cross-links induced by bis-chloroethylnitrosourea, but not those induced by nitrogen mustard. Once formed, chloroethylnitrosourea-induced cross-links are not broken by the enzyme. In agreement with deductions from experiments with living cells, it is concluded that chloroethylnitrosourea act by forming reactive monoadducts at the O6 position of guanine and/or the O4 position of thymine, which subsequently generate -CH2CH2- bridges to the complementary DNA strand. A new method for quantitating interstrand cross-links in DNA has been employed.

Original publication

DOI

10.1093/nar/11.22.7743

Type

Journal article

Journal

Nucleic Acids Res

Publication Date

25/11/1983

Volume

11

Pages

7743 - 7758

Keywords

Alkylation, Carmustine, Coliphages, DNA Repair, DNA, Bacterial, DNA, Viral, Escherichia coli, Kinetics, Methylnitronitrosoguanidine, Methyltransferases, O(6)-Methylguanine-DNA Methyltransferase, Tritium