Editing Ribonucleotide (section)

===Ribonucleotide discrimination===
During DNA synthesis, DNA polymerases must select against ribonucleotides, present at much higher levels compared with deoxyribonucleotides. It is crucial that there is selectivity as DNA replication has to be accurate to maintain the organism's genome. It has been shown that the active sites of Y-family DNA polymerases are responsible for maintaining a high selectivity against ribonucleotides.<ref>{{cite journal |last1=Kirouac |title=Structural Mechanism of Ribonucleotide Discrimination by a Y-Family DNA Polymerase|journal=Journal of Molecular Biology|date=1 April 2011|volume=407|issue=3|pages=382–390|doi=10.1016/j.jmb.2011.01.037|pmid=21295588|first1=Kevin N.|last2=Suo|first2=Zucai|last3=Ling|first3=Hong}}</ref> Most DNA polymerases are also equipped to exclude ribonucleotides from their active site through a bulky side chain residue that can sterically block the 2'-hydroxyl group of the ribose ring. However, many nuclear replicative and repair DNA polymerases incorporate ribonucleotides into DNA,<ref>{{cite journal |last1=Nick McElhinny |first1=SA |last2=Kumar |first2=D |last3=Clark |first3=AB |last4=Watt |first4=DL |last5=Watts |first5=BE |last6=Lundström |first6=EB |last7=Johansson |first7=E |last8=Chabes |first8=A |last9=Kunkel |first9=TA |title=Genome instability due to ribonucleotide incorporation into DNA. |journal=Nature Chemical Biology |date=October 2010 |volume=6 |issue=10 |pages=774–81 |doi=10.1038/nchembio.424 |pmid=20729855|pmc=2942972 }}</ref><ref>{{cite journal |last1=Nick McElhinny |first1=SA |last2=Watts |first2=BE |last3=Kumar |first3=D |last4=Watt |first4=DL |last5=Lundström |first5=EB |last6=Burgers |first6=PM |last7=Johansson |first7=E |last8=Chabes |first8=A |last9=Kunkel |first9=TA |title=Abundant ribonucleotide incorporation into DNA by yeast replicative polymerases. |journal=Proceedings of the National Academy of Sciences of the United States of America |date=16 March 2010 |volume=107 |issue=11 |pages=4949–54 |doi=10.1073/pnas.0914857107 |pmid=20194773|pmc=2841928 |bibcode=2010PNAS..107.4949N |doi-access=free }}</ref> suggesting that the exclusion mechanism is not perfect.<ref>{{cite journal|last=Kasiviswanathan|first=R|author2=Copeland, WC |title=Ribonucleotide discrimination and reverse transcription by the human mitochondrial DNA polymerase.|journal=The Journal of Biological Chemistry|date=Sep 9, 2011|volume=286|issue=36|pages=31490–500|pmid=21778232|doi=10.1074/jbc.M111.252460|pmc=3173122|doi-access=free}}</ref>