Histones are very highly conserved proteins and packaging the genome was the primary function previously associated with them. However, discovery of sequence divergent forms of the core histones, known as histone variants, along with the various post-translational modifications (PTM’s) that histones undergo changed this perspective.

Epigenetic changes like histone post translational modifications and change in chromatin architecture are key events that regulate gene expression. The N-terminal tail of histones can be modified by acetylation, phosphorylation, methylation, sumoylation, ubiquitination etc. This is an orchestrated event of “Writers” (that add modifications), “Readers” (that recognize the modification) and “Erasers” (that remove the modifications). This create an epigenetic mechanism for the regulation of a variety of normal and disease related processes by influencing and regulating gene transcription.

Previous studies in different models from yeast to human cells imply that chromatin structure serves as a barrier for repair at DNA damage sites. The complex array of histone modifications/variants alter the overall charge and conformation of chromatin which helps in recruitment of factors at damage site to facilitate repair, and thus in maintaining genomic integrity in response to DNA damaging agents.