Touch, act and go: landing and operating on nucleosomes.

Chromatin-associated enzymes are responsible for the installation, removal and reading of precise post-translation modifications on DNA and histone proteins. They are specifically recruited to the target gene by associated factors, and as a result of their activity, they contribute in modulating cell identity and differentiation. Structural and biophysical approaches are broadening our knowledge on these processes, demonstrating that DNA, histone tails and histone surfaces can each function as distinct yet functionally interconnected anchoring points promoting nucleosome binding and modification. The mechanisms underlying nucleosome recognition have been described for many histone modifiers and related readers. Here, we review the recent literature on the structural organization of these nucleosome-associated proteins, the binding properties that drive nucleosome modification and the methodological advances in their analysis. The overarching conclusion is that besides acting on the same substrate (the nucleosome), each system functions through characteristic modes of action, which bring about specific biological functions in gene expression regulation.