Bacteriophage T2 and T4, dam+ and damh and Eco dam+ methylation: preference at different sites.

We present a method for determining preference for methylation at minor methylation sites. The target DNA sequence is first subjected to computer-assisted analysis to predict which restriction endonuclease(s) will generate fragments that will contain only one or two likely minor methylation site(s). The target DNA is then methylated in vitro with a radioactive methyl-group donor and subjected to digestion by the chosen restriction enzyme(s). The amount of radioactivity in the various fragments is determined, after separating them using polyacrylamide gel electrophoresis. We documented the effect of nearby bases on the methylation preference and the relative preference for methylation at some specific minor methylation sites.