The d-isoAsp-25 variant of histone H2B is highly enriched in active chromatin: potential role in the regulation of gene expression?

Approximately 12 % of histone H2B in mammalian brain contains an unusual d-aspartate residue in its N-terminal tail. Most of this d-aspartate is linked to the C-flanking glycine via an isopeptide bond. To explore the possible significance of these modifications, we generated an antibody to the d-isoaspartyl form of H2B, and used it to assess its levels in H2B associated with active vs. silent chromatin. We found that the d-isoaspartyl form of H2B appears to be highly enriched in the former. This irreversible modification could serve a novel regulatory function in gene expression.