An estrogen-dependent demethylation at the 5' end of the chicken vitellogenin gene is independent of DNA synthesis.

A HpaII site 611 base pairs upstream from the 5' end of the chicken vitellogenin II gene exhibits an estrogen-dependent demethylation in hormone-responsive cells. The complete demethylation of this site occurs considerably later than the transcriptional activation of the gene, and therefore appears to be an effect rather than a cause of this activation. In vivo studies using two inhibitors of DNA synthesis (cytosine arabinoside and hydroxyurea) demonstrate that activation of transcription of the gene is independent of DNA synthesis. Surprisingly, the estrogen-dependent demethylation of the HpaII site is also independent of DNA synthesis. The possible involvement of a site-specific demethylase is discussed.