| Popis: |
SUMMARYNuclear processes depend on the organization of chromatin, whose basic units are cylinder-shaped complexes called nucleosomes. A subset of mammalian nucleosomesin situ(inside cells) resembles the canonical structure determinedin vitro25 years ago. Nucleosome structurein situis otherwise poorly understood. Using cryo-ET and 3-D classification analysis of budding yeast cells, here we find that canonical nucleosomes account for less than 10% of total nucleosomes expectedin situ. In a strain in which H2A-GFP is the sole source of histone H2A, class averages that resemble canonical nucleosomes both with and without GFP densities are foundex vivo(in nuclear lysates), but notin situ. These data suggest that the budding yeast intranuclear environment favors multiple non-canonical nucleosome conformations. Using the structural observations here and the results of previous genomics and biochemical studies, we propose a model in which the average budding yeast nucleosome’s DNA is partially detachedin situ. |
