Non-random spontaneous chain breakages occur in DNA methylated with dimethyl sulfate

Abstract
The method of in vivo footprinting uses partial methylation of the DNA in living cells with dimethyl sulfate (DMS), cleavage of the DNA chains at modified guanosines with piperidine, and mapping of the site of cleavage by the genomic sequencing technique of Church and Gilbert. Here we report on a spontaneous breakage reaction of DMS-methylated DNA at guanosines as well as adenosines, which is highly non-random with respect to the DNA sequence. In our in vivo genomic footprinting studies at the chicken lysozyme promoter this reaction gave rise to additional adenosine-derived bands in the guanosine sequence ladder