In oviparous vertebrates, egg yolk proteins such as vitellogenin are produced in the liver whereas the egg white proteins are synthesized in the oviduct. In the liver, vitellogenin genes are under the direct control of estradiol. In immature chicken or roosters the primary stimulation of vitellogenin gene by estradiol is characterized by a time lag before the onset of transcription. During this time lag there is a demethylation of the upper strand of the promoter region which is followed 24 hours later by the demethylation of the complementary strand. MDBP-2-H1 is a truncated histone H1 repressor that binds preferentially to the methylated promoter region of the vitellogenin gene or any other methylated sequence. Only the phosphorylated form of MDBP-2-H1 binds selectively to methylated DNA and estradiol causes a dephosphorylation of MDBP-2-H1. The unprotected methylated DNA becomes then the target for active demethylation. Active DNA demethylation occurs through a 5- MeC-DNA glycosylase in combination with a CpG rich RNA.