Primary & Secondary Coiling
          
        
         
   
              The DNA double
                helix is wrapped twice around a core unit of eight histone proteins.
              These nucleosomes
              are separated by a run of spacer DNA complexed with a
              single H1 histone
              unit.
              
            
      
Figure © 1997 by
        Klug & Cummings ; text © 2014 by Steven
          M. Carr