nucleosome

Introduction

Repeating motif consisting of 146-147 base pairs of DNA wrapped around a histone octomer in left handed superhelix. The histone octomer of nucleosomes contains 2 molecules each of H2A, H2B, H3 & H4 assembled in one H3-H4 heterotetramer & 2 H2A-H2B heterodimers. Nucleosomes wrap & compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Nucleosomes can be in open or closed formation affecting accessibility to sequence specific transcription factors & DNA dependent enzymes such as RNA & DNA polymerases. Histones & nucleosomes thereby play a central role in transcription regulation, DNA repair, DNA replication & chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, & nucleosome remodelling.

More general terms

• DNA motif
• molecular complex

Component of

• solenoid