Modification of nucleosome arrangements. (a) Nucleosome position can be altered by chromatin remodeling complexes that move, eject, or replace nucleosomes. (b) Histone modifying enzymes attach chemical groups to specific amino acid residues of nucleosome subunits, as indicated by small circles attached to histones. If the outcome is a direct result of the modification, such as making the chromatin structure more open, the modification is acting in cis. If the modification attracts another protein (blue) that performs the histone-