Subtelomeres are responsible to block heterochromatin from getting into the euchromatin region. Chromatin is found in two varieties&colon; euchromatin and heterochromatin. H4K16Ac also has roles in transcriptional activation and the maintenance of euchromatin. This lighter staining is due to the less compact structure of euchromatin. TERRA can also regulate telomere length by increasing euchromatin formation. The former (euchromatin) is lightly packed and rich in genes under active transcription. Typically, acetylation of histones is associated with euchromatin formation. Such DNA repair occurs in heterochromatin as well as in euchromatin. Relaxed, transcriptionally active DNA is referred to as euchromatin. In general, histone acetylation is linked to transcriptional activation and associated with euchromatin. In FSHD, the heterochromatin structure is lost, becoming euchromatin. Active chromatin may also be called euchromatin. Loose coiling, or euchromatin, is associated with higher levels of gene expression. Euchromatin participates in the active transcription of DNA to mRNA products. Euchromatin comprises the most active portion of the genome within the cell nucleus.