5-Methylcytosine is a hotspot for mutation

Methylcytosine hotspots in E. coli. Nonsense mutations at 15 different sites in lacl were scored. All resulted in G · C → A · T transitions. The asterisk (*) marks the positions of 5-methylcytosines, and the white bars mark sites where transitions known to occur were not isolated in this group.

[Data from C. Coulondre, J. H. Miller, P. J. Farabaugh, and W. Gilbert, “Molecular Basis of Base Substitution Hotspots in Escherichia coli,” Nature 274, 1978, 775.]