Editing Processivity (section)

==Polymerase processivities==
Multiple DNA polymerases have specialized roles in the DNA replication process. In ''[[E. coli]]'', which replicates its entire [[genome]] from a single replication fork, the polymerase [[Pol III|DNA Pol III]] is the enzyme primarily responsible for DNA replication and forms a replication complex with extremely high processivity. The related [[Pol I|DNA Pol I]] has [[exonuclease]] activity and serves to degrade the [[RNA primer]]s used to initiate DNA synthesis. Pol I then synthesizes the short DNA fragments in place of the former RNA fragments. Thus Pol I is much less processive than Pol III because its primary function in DNA replication is to create many short DNA regions rather than a few very long regions.

In [[eukaryote]]s, which have a much higher diversity of DNA polymerases, the low-processivity initiating enzyme is called [[DNA polymerase alpha|Pol α]], and the high-processivity extension enzymes are [[DNA polymerase delta|Pol δ]] and [[DNA polymerase epsilon|Pol ε]]. Both [[prokaryote]]s and eukaryotes must "trade" bound polymerases to make the transition from initiation to elongation. This process is called polymerase switching.<ref name=tsurimoto>{{cite journal|last1=Tsurimoto|first1=Toshiki|last2=Stillman|first2=Bruce|title=Replication Factors Required for SV40 DNA Replication in Vitro|journal=J Biol Chem|date=1991|volume=266|issue=3|pages=1961–1968|doi=10.1016/S0021-9258(18)52386-3|url=http://www.jbc.org/content/266/3/1961.short|access-date=23 November 2014|pmid=1671046|doi-access=free}}</ref><ref>{{cite journal|last1=Maga|first1=Giovanni|last2=Stucki|first2=Manuel|last3=Spadari|first3=Silvio|last4=Hübscher|first4=Ulrich|title=DNA polymerase switching: I. Replication factor C displaces DNA polymerase α prior to PCNA loading|journal=Journal of Molecular Biology|date=January 2000|volume=295|issue=4|pages=791–801|doi=10.1006/jmbi.1999.3394|pmid=10656791}}</ref>