DNA methylase from Pisum sativum.

DNA methylase activity was detected in nuclei from pea shoots. The enzyme can only be extracted by low-salt treatment if the nuclei are pretreated with micrococcal nuclease. Only a single enzyme was detected, and it was purified to a specific activity of 1620 units/mg of protein.

Eukaryotic DNA methylases and their use for in vitro methylation.

DNA methylases from mouse and pea have been purified and characterized. Both are high molecular mass enzymes that show greater activity with hemimethylated than unmethylated substrate DNA. Both methylate cytosines in CpG preferentially, but not exclusively and show similar kinetics of methylation, which makes it difficult to saturate all possible sites on the DNA, but procedures are described that circumvent this problem.