Miscoding by the Exocyclic and Related DNA Adducts 3,N⁴-Etheno-2^'-deoxycytidine, 3,N⁴-Ethano-2'-deoxycytidine, and 3-(2-Hydroxyethyl)-2'-deoxyuridine

3,N⁴-Etheno-2'-deoxycytidine, 3-(hydroxyethyl)-2'-deoxyuridine, and 3,N⁴-ethano-2'-deoxycytidine are found in DNA of cells treated with either vinyl chloride or 1,3-bis(2-chloroethyl)-nitrosourea. These exocyclic and related DNA adducts were incorporated into oligodeoxynucleotides, which were then used as templates for primer extension in reactions catalyzed by the Klenow fragment of Escherichia coli DNA polymerase I. The miscoding potential of each lesion was determined quantitatively. DNA primers were readily extended on an ∊dC-modified template; dAMP and dTMP were incorporated opposite the lesion. With high concentrations of DNA polymerase, small amounts of fully extended reaction products containing dAMP and dGMP or one-base and two-base deletions opposite ethano-dC were formed. Primer extension was blocked partially on templates containing 3-(hydroxyethyl)-dU; dAMP and smaller amounts of dTMP and dCMP were incorporated. The frequencies of nucleotide insertion opposite each of the three lesions and the frequencies of chain extension from the 3'-primer terminus, determined by kinetic analysis, were consistent with results of experiments utilizing polyacrylamide gel electrophoresis. We conclude from these studies that ∊dC, ethano-dC, and 3-(hydroxyethyl)-U are potentially miscoding lesions; only ∊dC facilitates translesional synthesis.