In contrast to old H3 and H4, the old H2A and H2B histone proteins are released and degraded; therefore, newly assembled H2A and H2B proteins are incorporated into new nucleosomes. H2A and H2B are assembled into dimers which are then loaded onto nucleosomes by the nucleosome assembly protein-1 (NAP-1) which also assists with nucleosome sliding. The nucleosomes are also spaced by ATP-dependent nucleosome-remodeling complexes containing enzymes such as Isw1 Ino80, and Chd1, and subsequently assembled into higher order structure.