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  • Title: Base incorporation and extension at a site-specific ethenocytosine by Escherichia coli DNA polymerase I Klenow fragment.
    Author: Simha D, Yadav D, Rzepka RW, Palejwala VA, Humayun MZ.
    Journal: Mutat Res; 1994 Jan 16; 304(2):265-9. PubMed ID: 7506370.
    Abstract:
    Ethenocytosine (epsilon C) is a highly mutagenic exocyclic DNA lesion induced by carcinogens vinyl chloride and urethane. We have examined base incorporation and extension at a site-specific epsilon C residue by a quantitative gel electrophoretic assay using an exonuclease-deficient version of Escherichia coli DNA polymerase I (Klenow fragment) as the model enzyme. The data show that the KM for incorporation of adenine or thymine opposite epsilon C by is about 5 orders of magnitude higher than that for the incorporation of guanine opposite normal cytosine. The KM for base extension past epsilon C:A and epsilon C:T pairs is 1-2 orders of magnitude higher than that observed for a C:G pair. Although adenine misinsertion is favored over that of thymine, base extension occurs more readily when the base incorporated opposite epsilon C is thymine.
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