How does the histone code work?

Patterns of histone post-translational modifications correlate with distinct chromosomal states that regulate access to DNA, leading to the histone-code hypothesis. However, it is not clear how modification of flexible histone tails leads to changes in nucleosome dynamics and, thus, chromatin structure. The recent discovery that, like the flexible histone tails, the structured globular domain of the nucleosome core particle is also extensively modified adds a new and exciting dimension to the histone-code hypothesis, and calls for the re-examination of current models for the epigenetic regulation of chromatin structure. Here, we review these findings and other recent studies that suggest the structured globular domain of the nucleosome core particle plays a key role regulating chromatin dynamics.