Editing Exonuclease (section)

==Significance to polymerase==

RNA [[polymerase]] II is known to be in effect during transcriptional termination; it works with a 5' exonuclease (human gene Xrn2) to degrade the newly formed transcript downstream, leaving the polyadenylation site and simultaneously shooting the polymerase. This process involves the exonuclease's catching up to the pol II and terminating the transcription.<ref>{{cite journal | author = Hage A EL | title = Efficient termination of transcription by RNA polymerase I requires the 5′ exonuclease Rat1 in yeast | journal = Genes Dev. | volume = 22 | pages = 1068–081| year = 2008 |doi=10.1101/gad.463708 |pmid=18413717 | issue = 8 | pmc = 2335327 |display-authors=etal}}</ref>

[[DNA polymerase I|Pol I]] then synthesizes DNA nucleotides in place of the RNA primer it had just removed. DNA polymerase I also has 3' to 5' and 5' to 3' exonuclease activity, which is used in editing and proofreading DNA for errors. The 3' to 5' can only remove one mononucleotide at a time, and the 5' to 3' activity can remove mononucleotides or up to 10 nucleotides at a time.