ABSTRACT

It was not long ago that chromatin was widely regarded as adding more ‘‘structure’’ to DNA, but not ‘‘function.’’ Today, it is broadly perceived that chromatin modifications occur locally, in a regulated manner, to create different microenvironments along the chromatin fiber. Accordingly, these chromatin-governed microenvironments regulate-positively or negatively-the interaction between DNA and other protein players. Histone tails play a key role in these mechanisms. They provide the substrate, usually a stretch of a few aminoacids that extend out from the nucleosome towards the nucleoplasm, to accommodate post-translational modifications (1). Recently, it has been shown that this general theme applies also in the case of double-strand breaks introduced into cellular DNA.