The in Vitro Methylation of DNA by a Minor Groove Binding Methyl Sulfonate Ester

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Abstract
The preparation of sequence and groove specific DNA methylating agents based on N-methylpyrrolecarboxamide subunits appended with an O-methyl sulfonate ester functionality (MeOSO2(CH2)2-Lex) has previously been described [Zhang, Y., Chen, F.-X., Mehta, P., and Gold, B. (1993) Biochemistry32, 7954−7965]. In contrast to simple methyl sulfonate esters, e.g., methyl methanesulfonate (MMS), which predominantly methylate at 7-guanine, MeOSO2(CH2)2-Lex affords N3-methyladenine (3-MeAde) as its major adduct. Using competitive ELISA determinations, the methylation at major and minor groove sites in calf thymus DNA by MeOSO2(CH2)2-Lex has been precisely quantitated. The yields of N7-methylguanine (7-MeGua), 3-MeAde, and O6-methyldeoxyguanosine (6-Me-dGuo) are 0.424, 3.195, and 0.0027 mmol of adduct/mol of DNA, respectively, using 10 μM MeOSO2(CH2)2-Lex and 100 μM DNA. This compares to 0.773, 0.072, and 0.0033 mmol of adduct/mol of DNA for 7-MeGua, 3-MeAde, and 6-Me-dGuo, respectively, using MMS. The increase in the yield of 3-MeAde due to the minor groove equilibrium binding properties of MeOSO2(CH2)2-Lex is ∼40-fold relative to MMS.