Editing S phase (section)

== Nucleosome replication ==
[[File:NucleosomeDuplication.png|thumb|239x239px|Conservative reassembly of core H3/H4 nucleosome behind the replication fork.|alt=]]
Free histones produced by the cell during S-phase are rapidly incorporated into new nucleosomes. This process is closely tied to the replication fork, occurring immediately in “front” and “behind” the replication complex. Translocation of MCM helicase along the leading strand disrupts parental nucleosome octamers, resulting in the release of H3-H4 and H2A-H2B subunits.<ref name=":8">{{cite journal | vauthors = Ramachandran S, Henikoff S | title = Replicating Nucleosomes | journal = Science Advances | volume = 1 | issue = 7 | pages = e1500587 | date = August 2015 | pmid = 26269799 | pmc = 4530793 | doi = 10.1126/sciadv.1500587 | bibcode = 2015SciA....1E0587R }}</ref> Reassembly of nucleosomes behind the replication fork is mediated by chromatin assembly factors (CAFs) that are loosely associated with replication proteins.<ref name=":2" /><ref name=":9">{{cite journal | vauthors = Annunziato AT | title = Split decision: what happens to nucleosomes during DNA replication? | journal = The Journal of Biological Chemistry | volume = 280 | issue = 13 | pages = 12065–8 | date = April 2005 | pmid = 15664979 | doi = 10.1074/jbc.R400039200 | doi-access = free }}</ref> Though not fully understood, the reassembly does not appear to utilize the [[Semiconservative replication|semi-conservative]] scheme seen in DNA replication.<ref name=":9" /> Labeling experiments indicate that nucleosome duplication is predominantly conservative.<ref name=":9" /><ref name=":8" /> The paternal H3-H4 core nucleosome remains completely segregated from newly synthesized H3-H4, resulting in the formation of nucleosomes that either contain exclusively old H3-H4 or exclusively new H3-H4.<ref name=":8" /><ref name=":9" /> “Old” and “new” histones are assigned to each daughter strand semi-randomly, resulting in equal division of regulatory modifications.<ref name=":8" />