Nano-Scale Observation of Higher-Order Genome Structure Reconstituted from DNA and Chromosome Proteins

In order to analyze chromatin higher-order structures, we have developed an experimental system to assemble long nucleosomal fibers and linker histone H1-induced thicker fibers from DNA and purified histones. We reconstituted chromatin fibers using normal, tailless, and hyper-acetylated core histones to reveal the effect of histone tail on the higher-order assembly of nucleosomes. AFM observation of these nucleosomes revealed that the interaction between nucleosomes decreased both by hyper-acetylation and the removal of the tails. The formation of H1-induced thick fiber was also affected by the acetylation and the tail-removal. The nucleosomes with hyper-acetylated core histones formed a thinner fiber, and the tailless nucleosome could not form any further fibrous structures by H1. These results suggested that the histone tail has a critical role in nucleosome-nucleosome interaction, which is required for the formation of H1-induced 30-nm fibers.