Mesoscale organization of the chromatin fiber.

The proper organization of the physical genome is essential to facilitate DNA-templated processes from transcription to replication to DNA repair. Genome-wide studies over the past two decades have provided us with a detailed understanding of the positions and modification states of nucleosomes across the genomes of many organisms, as well as an increasingly mature understanding of chromosome organization at the kilobase to megabase scale. Here, we explore chromatin organization at intermediate scales of ∼2-10 nucleosomes, from early views supporting a secondary structural element known as the 30nm fiber to more recent 'sea of nucleosomes' models.