Prototropic changes in cationic base-pair adducts. II. Guanine methylation

AM 1 calculations have been used to study the effects of CH attachment on the structures, energies, and, in some cases, proton transfer reactions of guanine cytosine base pairs. Methylation of both the guanine 3- and O⁶-positions is predicted to lead to chemically significant concentrations of intermediate base pairs arising from proton transfer from the guanine 1- to the cytosine 3-position. The possible biological implications of such intermediates in nucleic acids is discussed in relation to the formation of either doubly abasic sites or abasic sites opposite potentially miscoding DNA lesions. © 1992 John Wiley & Sons, Inc.