Heterogeneity of DNA methylation in murine L5178Y lymphoblasts.

Comparison of the extent of methylation in mouse DNA fragments rendered MgCl2 soluble after mild DNase II digestion of nuclei, with different reassociation rate and nucleoli-bound, revealed the existence of 3 regions of the genome particularly 5-methylcytosine-rich: the sequences considered to be related to the transcriptionally active chromatin with the highest content of this base and fast reassociating, as well as nucleolar DNA with somewhat lower proportion of the methylated cytosines.