Sequence specificity of DNA repair by Escherichia coli Fpg protein

The sequence specificity of guanine methylation in DNA by N-methyl-N-nitrosourea and the subsequent repair of rung-opened N7-methylguanine was studied using oligonucleotides of defined sequence. It was found that the methylation of TAGGGGCCCCTA was <2-fold greater than that occuring in TAGAGATCTCTA or TATGTGCACATA and 6-fold greater than in TACGCGCGCGTA. This is consistent with the concept that guanine methylation is least when the 5' preceding base is a pyrimidine and greatest when the 5' base is another guanine