Figure 1. Nucleosome structure.

Figure 1

Nucleosome structure. Cartoon representation of the structure of the nucleosome based on the X-Ray crystal structure.7 Nucleosomes are assembled in a stepwise manner from 146 bp of DNA which first recruits two histone H3/H4 dimers to form a tetramer and then two histone H2A/H2B dimers to form the histone octamer. In a nucleosome, the DNA makes 1.7 turns around the histone octamer. In the side-view of a nucleosome presented here, we have depicted the nearest 0.85 coil of DNA (73 bp) in black and the far-side 0.85 coil of DNA in grey. In the exploded view at the bottom, where the upper and lower faces of the nucleosome are separated, it can be seen that a nucleosome comprises two symmetrical halves. Each half contains one molecule of each of the four core histones which each make two major contacts with the DNA. The positively charged lysine-rich histone tails do not adopt a rigid structure but extend out from the nucleosome and have the potential to wrap around the DNA.

From: Chromatin Mechanisms Regulating Gene Expression In Health And Disease

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