Newly Synthesized Histones: Passive or Active Players in the Regulation of Epigenetic Inheritance?

In the wake of a replication fork, nascent chromatin is composed of a 1:1 mixture of parental histones and newly synthesized histones. The parental histones contain the pattern of post-translational modifications that dictated the chromatin state prior to DNA replication. The parental histones clearly play a critical role in epigenetic inheritance as they serve as the template that directs the maturation of the nascent chromatin into the appropriate mature chromatin state. An essential step that ensures faithful epigenetic inheritance is the transfer of the parental histone modification state to the newly synthesized histones. But what of the newly synthesized histones that make up 50% of nascent chromatin? Are they merely blank slates or do they play an active role in epigenetic inheritance? This review will address this question by exploring the nature of newly synthesized histones and their contribution to the assembly of specific chromatin states.