Role of nucleosome positioning in 3D chromatin organization and loop formation

We present a physics-based polymer model that can investigate 3D organization of chromatin accounting for DNA elasticity,DNA-bending due to nucleosomes, and 1D organization of nucleosomes along DNA. We find that the packing density ofchromatin oscillates between densities corresponding to highly folded and extended configurations as we change thenucleosome organization (length of linker DNA). We compute the looping probability of chromatin and show that thepresence of nucleosomes increases the looping probability of the chain compared to that of a bare DNA. We also show thatlooping probability has a large variability depending on the nature of nucleosome organization and density of linker histones.