DNA methylation in chromatin fractions of chick embryo cells.

Transcriptionally active chromatin was prepared from cultured fibroblasts of chick embryos by fractionation after partial digestion with DNAase II. The degree of DNA methylation in the active chromatin fraction is twice that of inactive or unfractionated chromatin in unsynchronized cells and 4 to 5 times greater at the beginning of the S-phase in synchronized cells.