Polynucleotide Phosphorylase | |||||||||
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Identifiers | |||||||||
EC no. | 2.7.7.8 | ||||||||
CAS no. | 9014-12-4 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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Polynucleotide Phosphorylase (PNPase) is a bifunctional enzyme with a phosphorolytic 3' to 5' exoribonuclease activity and a 3'-terminal oligonucleotide polymerase activity.[2] That is, it dismantles the RNA chain starting at the 3' end and working toward the 5' end.[1] 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.[1] 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 was disproven by the late 1950s.[3][4]
It is involved in mRNA processing and degradation in bacteria, plants,[5] and animals.[6]
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 a K-homology domain. The protein is present in bacteria and in the chloroplasts[2] and mitochondria[7] of some eukaryotic cells. In eukaryotes and archaea, a structurally and evolutionary related complex exists, called the exosome complex.[7]
The same abbreviation (PNPase) is also used for another, otherwise unrelated enzyme, Purine nucleoside phosphorylase.
Human PNPase I | |||||||
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Identifiers | |||||||
Symbol | PNPASE | ||||||
Alt. symbols | PNPase, OLD35, old-35 | ||||||
NCBI gene | 87178 | ||||||
HGNC | 23166 | ||||||
OMIM | 610316 | ||||||
PDB | 1E3P | ||||||
RefSeq | NM_033109 | ||||||
UniProt | Q8TCS8 | ||||||
Other data | |||||||
EC number | 2.7.7.8 | ||||||
Locus | Chr. 2 p15 | ||||||
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