DNA methylation can enhance or induce DNA curvature

Oligomers of different palindromic sequences (EcoRI, BamHI, and ClaI linkers) were ligated to form distributions of multimers. These long ligation ladders were methylated using corresponding methylases. The migration of the unmethylated as well as the methylated multimer distributions was analysed in 10% polyacrylamide gels. The migration anomaly of these sequences is interpreted in terms of the curvature of the DNA helix axis. The double-stranded oligomer dCGGAATTCCG is considerably curved in its unmodified form. Its curvature is strongly enhanced when the central dAs are methylated. This result is predicted by a model for DNA curvature. Multimers of the closely related sequence dCGGGATCCCG are straight. When methylated at the central dAs or at the most central dCs, a small curvature of the helix axis is induced. The double-stranded oligomer dCCATCGATGG is straight in its unmodified form as well as when it is methylated. Thus, DNA curvature can be induced or enhanced by methylation. However, DNA methylation at palindromic sequences seems not always to influence the linear path of the DNA helix axis.