The spread of epigenetic states after replication. (a) The open state may be propagated through the binding of a bromodomain-containing complex that also contains a HAT subunit, which acetylates the same residues in neighboring histone octamers. (b) The closed state may be spread through binding of HP1, which reassociates with parental histones after replication and is associated with the repressed state of tightly packed heterochromatin. HP1 contains a chromodomain that binds methylated Lys residues in histones and the chromodomain also recruits a methyltransferase to propagate the parental methylation pattern in neighboring new histones.