The 5-methylcytosine content of highly repeated sequences in human DNA

Abstract

Previously, we found much tissue-or cell-specificity in the levels of 5-methylcytosine (m5C) in the total human genome as well as in DNA fractions resolved by reaasociation kinetics. We now report that there were even greater differences in the m5C content of the highly repeated, tandem EcoRI family of DNA sequences from different human organs or cell populations. The ratio of m5C levels in this DNA fraction from brain, placenta, and sperm was 2.0:1.2:1.0. At a HhaI site in this repeat family, sperm DNA was 5-10 fold less methylated than somatic DNAs. In contrast, the highly repeated Alu family, which is 5 of the genome, had almost the same high m C content in brain and placenta despite marked tissue-specific differences in m C levels of the single copy sequences with which these repeats are interspersed. These data show that very different degrees of change in methylation levels of various highly repeated DNA sequences accompany differentiation © 1983 IRL Press Limited.