title: X inactivation, differentiation, and DNA methylation.
abstract: A model based on DNA methylation is proposed to explain the initiation and maintenance of mammalian X inactivation and certain aspects of other permanent events in eukaryotic cell differentiation. A key feature of the model is the proposal of sequence-specific DNA methylases that methylate unmethylated sites with great difficulty but easily methylate half-methylated sites. Although such enzymes have not yet been detected in eukaryotes, they are known in bacteria. An argument is presented, based on recent data on DNA-binding proteins, that DNA methylation should affect the binding of regulatory proteins. In support of the model, short reviews are included covering both mammalian X inactivation and bacterial restriction and modification enzymes.
mesh_terms: D000818:Animals; D004247:DNA / Q000378:metabolism*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D004261:DNA Replication; D008745:Methylation; D008958:Models, Molecular; D012728:Sex Chromatin; D012730:Sex Chromosomes / Q000378:metabolism*
chemical_list: D004247:DNA; D004248:DNA (Cytosine-5-)-Methyltransferases