Polynucleotide phosphorylase

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Structure of the PNPase trimer
Polynucleotide Phosphorylase
Identifiers
Symbol	PNPASE
Alt. Symbols	PNPase, OLD35, old-35
Entrez	87178
HUGO	23166
OMIM	610316
PDB	1E3P
RefSeq	NM_033109
UniProt	Q8TCS8
Other data
EC number	2.7.7.8
Locus	Chr. 2 p15

Polynucleotide Phosphorylase (PNPase) is bifunctional enzyme with a phosphorolytic 3' to 5' exoribonuclease activity and a 3'-terminal oligonucleotide polymerase activity.^[1] It is involved with mRNA processing and degradation in bacteria, plants,^[2] and in humans.^[3]

In humans, the enzyme is encoded by the 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 an K-homology domain. The protein is present in eubacteria and in the chloroplasts^[1] and mitochondria^[4] of some eukaryotic cells. In eukaryotes and archaebacteria, a structurally and evolutionary related complex exists, called the exosome ^[4].

Confusingly, the same abbreviation (PNPase), is also used for another, otherwise unrelated, enzyme, namely Purine nucleoside phosphorylase.

[edit] References

^ ^a ^b Yehudai-Resheff S, Hirsh M, Schuster G (2001). "Polynucleotide phosphorylase functions as both an exonuclease and a poly(A) polymerase in spinach chloroplasts". Mol. Cell. Biol. 21 (16): 5408–16. doi:10.1128/MCB.21.16.5408-5416.2001. PMID 11463823.
^ Yehudai-Resheff S, Zimmer SL, Komine Y, Stern DB (2007). "Integration of chloroplast nucleic acid metabolism into the phosphate deprivation response in Chlamydomonas reinhardtii". Plant Cell 19 (3): 1023–38. doi:10.1105/tpc.106.045427. PMID 17351118.
^ Sarkar D, Fisher PB (2006). "Human polynucleotide phosphorylase (hPNPase old-35): an RNA degradation enzyme with pleiotrophic biological effects". Cell Cycle 5 (10): 1080–4. PMID 16687933.
^ ^a ^b Schilders G, van Dijk E, Raijmakers R, Pruijn GJ (2006). "Cell and molecular biology of the exosome: how to make or break an RNA". Int. Rev. Cytol. 251: 159–208. doi:10.1016/S0074-7696(06)51005-8. PMID 16939780.

[edit] External links

v • d • e Transferases: Phosphotransferases/kinases (EC 2.7)

2.7.1 - OH acceptor	Hexo- - Gluco- - Fructo- (Hepatic fructo-) - Galacto- - Phosphofructo- (1, 2) - Riboflavin - Shikimate - Thymidine - NAD⁺ - Glycerol - Pantothenate - Mevalonate - Pyruvate - Deoxycytidine - PFP - Diacylglycerol - Bruton's tyrosine - Phosphoinositide 3 (Class I PI 3, Class II PI 3) - Sphingosine

2.7.2 - COOH acceptor	Phosphoglycerate - Aspartate

2.7.3 - N acceptor	Creatine

2.7.4 - PO₄ acceptor	Phosphomevalonate - Adenylate - Nucleoside-diphosphate

2.7.6 - P₂O₇	Ribose-phosphate diphosphokinase - Thiamine pyrophosphokinase

2.7.7 - nucleotidyl-	Integrase - PNPase - Polymerase - RNase PH - UDP-glucose pyrophosphorylase - Galactose-1-phosphate uridylyltransferase -Terminal deoxynucleotidyl transferase - RNA replicase - Reverse transcriptase (Telomerase) - Transposase

2.7.8 - other phos.	N-acetylglucosamine-1-phosphate transferase

2.7.10-11 - protein	Tyrosine - Serine/threonine-specific