Polynucleotide phosphorylase: Difference between revisions
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| caption = Structure of the PNPase trimer from ''Streptomyces antibioticus''. [[Protein–protein interaction|PDB]] 1e3p.<ref name="pmid11080643">{{cite journal | vauthors = Symmons MF, Jones GH, Luisi BF | title = A duplicated fold is the structural basis for polynucleotide phosphorylase catalytic activity, processivity, and regulation | journal = Structure | volume = 8 | issue = 11 | pages = 1215–26 | date = November 2000 | pmid = 11080643 | doi = 10.1016/S0969-2126(00)00521-9 }}</ref>
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'''Polynucleotide Phosphorylase''' ('''PNPase''') is a bifunctional [[enzyme]] with a [[phosphorolysis|phosphorolytic]] 3' to 5' [[exoribonuclease]] activity and a 3'-terminal [[oligonucleotide]] [[polymerase]] activity.<ref name="pmid11463823">{{cite journal | vauthors = Yehudai-Resheff S, Hirsh M, Schuster G | title = Polynucleotide phosphorylase functions as both an exonuclease and a poly(A) polymerase in spinach chloroplasts | journal = Molecular and Cellular Biology | volume = 21 | issue = 16 | pages = 5408–16 | date = August 2001 | pmid = 11463823 | pmc = 87263 | doi = 10.1128/MCB.21.16.5408-5416.2001 }}</ref> That is, it dismantles the RNA chain starting at the 3' end and working toward the 5' end.<ref name="pmid11080643" /> It also synthesizes long, highly heteropolymeric tails ''in vivo''. It accounts for all of the observed residual [[polyadenylation]] in strains of ''Escherichia coli'' missing the normal polyadenylation enzyme.<ref name="pmid11080643"/> Discovered by [[Marianne Grunberg-Manago]] working in Severo Ochoa's lab in 1955, the RNA-polymerization activity of PNPase was initially believed to be responsible for DNA-dependent synthesis of messenger RNA, a notion that got disproved by the late 1950s.<ref>{{cite journal | vauthors = Grunberg-Manago M, Ortiz PJ, Ochoa S | title = Enzymic synthesis of polynucleotides. I. Polynucleotide phosphorylase of azotobacter vinelandii | journal = Biochimica et Biophysica Acta | volume = 20 | issue = 1 | pages = 269–85 | date = April 1956 | pmid = 13315374 | doi=10.1016/0006-3002(56)90286-4}}</ref><ref name="pmid13895983">{{cite journal | vauthors = Furth JJ, Hurwitz J, Anders M | title = The role of deoxyribonucleic acid in ribonucleic acid synthesis. I. The purification and properties of ribonucleic acid polymerase | journal = The Journal of Biological Chemistry | volume = 237 | issue = | pages = 2611–9 | date = August 1962 | pmid = 13895983 | doi = | url = http://www.jbc.org/content/281/15/e12.full.pdf }}</ref>
It is involved in [[mRNA processing]] and degradation in bacteria, plants,<ref name="pmid17351118">{{cite journal | vauthors = Yehudai-Resheff S, Zimmer SL, Komine Y, Stern DB | title = Integration of chloroplast nucleic acid metabolism into the phosphate deprivation response in Chlamydomonas reinhardtii | journal = The Plant Cell | volume = 19 | issue = 3 | pages = 1023–38 | date = March 2007 | pmid = 17351118 | pmc = 1867357 | doi = 10.1105/tpc.106.045427 }}</ref> and in humans.<ref name="Sarkar_2006">{{cite journal | vauthors =
In humans, the enzyme is encoded by the {{gene|PNPT1}} gene. In its active form, the protein forms a ring structure consisting of three PNPase molecules. Each PNPase molecule consists of two [[RNase PH]] domains, an S1 RNA binding domain and a [[Protein K (gene expression)|K-homology domain]]. The protein is present in [[bacteria]] and in the [[chloroplasts]]<ref name="pmid11463823"/> and [[mitochondria]]<ref name="pmid16939780">{{cite book | vauthors = Schilders G, van Dijk E, Raijmakers R, Pruijn GJ | title = Cell and molecular biology of the exosome: how to make or break an RNA | volume = 251 | pages = 159–208 | year = 2006 | pmid = 16939780 | doi = 10.1016/S0074-7696(06)51005-8 | isbn = 9780123646552 | series = International Review of Cytology }}</ref> of some [[eukaryotic]] cells. In eukaryotes and [[archaea]], a structurally and evolutionary related complex exists, called the ''[[exosome complex]]''.<ref name="pmid16939780"/>
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