Practice question

Biochemical reconstitution and high resolution crystal structures confirm nucleosome core particle comprises exactly eight histone proteins forming disc. Two copies each of canonical H2A, H2B, H3, H4 assemble as octamer shaping 11 nanometer particle. Central kernel forms H3-H4 tetramer via four-helix bundle through H3-H3 interface, while two H2A-H2B dimers dock on sides contacting outer DNA wraps. Six histones would destabilize wrapping, ten or twelve exceed structural capacity supported by stoichiometry measurements. Micrococcal nuclease protection and ultracentrifugation correspond to octamer alone, fundamental compaction unit conserved throughout eukaryotes.