The inactive X chromosome in the human female is enriched in 5-methylcytosine to an unusual degree and appears to contain more of this modified nucleotide than the remainder of the genome

J Genet. Apr-Aug 2003;82(1-2):13-6. doi: 10.1007/BF02715875.


By employing a procedure that combines ELISA and photoacoustic spectroscopy, we have examined the content of 5-methylcytosine (m(5)C) in DNA of individuals who differed from one another in the number of X chromosomes in their genomes. The results show that the human inactive X chromosome (Xi) contains very high amounts of this modified nucleotide. We estimate that in the 46,XX female there is more m(5)C in Xi (~ 3.6 x 10(7)) than in all the remaining chromosomes put together (~ 2.1 x 10(7)). Our results also suggest that nearly one-fifth of all cytosines in Xi are methylated and that, in addition to CpG methylation, there is extensive non-CpG methylation as well.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Methylcytosine / metabolism*
  • Chromosomes, Human, X*
  • CpG Islands
  • DNA / metabolism*
  • DNA Methylation
  • Dinucleotide Repeats
  • Female
  • Fetus / metabolism
  • Fibroblasts / metabolism
  • Genome, Human*
  • Humans
  • Lymphocytes / metabolism


  • 5-Methylcytosine
  • DNA