The role of mutagenic metal ions in mediating in vitro mispairing by alkylpyrimidines.
A variety of alkylating mutagens and carcinogens produce pyrimidine adducts in DNA that block DNA synthesis in vitro. Since DNA synthesis past the lesion is a necessary step to produce mutations, we investigated the role of the mutagenic metal ion Mn++ in facilitating DNA synthesis past alkylpyrimidines. In the presence of the natural metal activator Mg++, N3-ethyldeoxythymidine (N3-Et-dT) and O2-ethyldeoxythymidine (O2-Et-dT), present at a single site in DNA, blocked in vitro DNA synthesis 3' to the lesion and after incorporating dA opposite each lesion. The presence of Mn++ permitted postlesion synthesis with dT misincorporated opposite N3-Et-dT and O2-Et-dT, implicating these lesions in A.T-->T.A transversion mutagenesis. The DNA synthesis block by O4-ethyldeoxythymidine (O4-Et-dT) in the presence of Mg++ was partial and was also removed by Mn++. Consistent with in vivo studies, dG was incorporated opposite O4-Et-dT during postlesion synthesis, leading to A.T-->G.C transition mutagenesis. We also have discovered a new class of DNA adducts, N3-hydroxyalkyldeoxyuridine (3-HA-dU) lesions, which are produced by mutagenic and carcinogenic aliphatic epoxides. 3-HA-dU is formed after initial alkylation at the N3 position of dC followed by a rapid hydrolytic deamination. As observed with the analogous mutagenic N3-Et-dT, the ethylene oxide-induced 3-hydroxyethyldeoxyuridine (3-HE-dU) blocked in vitro DNA synthesis, which could be by-passed in the presence of Mn++. The nucleotide incorporated opposite 3-HE-dU during postlesion synthesis is being identified. These studies suggest a role for Mn++ in mediating mutagenic and carcinogenic effects of environmentally important ethylating agents and aliphatic epoxides.
Bhanot
O S
OS
Department of Environmental Medicine, New York University Medical Center, New York.
Solomon
J J
JJ
D000478:Alkylation; D000818:Animals; D001482:Base Composition / Q000187:drug effects*; D001483:Base Sequence; D004261:DNA Replication / Q000187:drug effects*; D020149:Manganese Poisoning; D008670:Metals / Q000633:toxicity*; D008969:Molecular Sequence Data; D009153:Mutagens / Q000633:toxicity*; D011743:Pyrimidines / Q000378:metabolism*
D008670:Metals; D009153:Mutagens; D011743:Pyrimidines