image reconstruction to 22 a resolution of the histone octamer ( h3 ) 2 ( h4 ) 2 ( h2a ) 2 ( h2b ) 2 shows it to have a 2-fold axis of symmetry , and the overall shape of the left-handed helical spool on which to wind about two turns of a flat superhelix of dna in the nucleosome .
C0019646
h2a
C0028623
nucleosome