Polynucleotide phosphorylase

Polynucleotide Phosphorylase
File:Crystal structure 1E3P.jpg Structure of the PNPase trimer from Streptomyces antibioticus. PDB 1e3p.
Identifiers
EC number	2.7.7.8
CAS number	Template:CAS
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 / EGO
Search PMC articles PubMed articles NCBI proteins

Polynucleotide Phosphorylase (PNPase) is a bifunctional enzyme with a phosphorolytic 3' to 5' exoribonuclease activity and a 3'-terminal oligonucleotide polymerase activity. That is, it dismantles the RNA chain starting at the 3' end and working toward the 5' end. 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. Discovered by Ochoa in 1951, 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 (http://www.jbc.org/content/281/15/e12.full.pdf).

It is involved on mRNA processing and degradation in bacteria, plants, and in humans.

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 and mitochondria of some eukaryotic cells. In eukaryotes and archaea, a structurally and evolutionary related complex exists, called the exosome.

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

Model organisms

Pnpt1 knockout mouse phenotype

Characteristic	Phenotype
Homozygote viability	Abnormal
Recessive lethal study	Abnormal
Fertility	Normal
Body weight	Normal
Anxiety	Normal
Neurological assessment	Normal
Grip strength	Normal
Hot plate	Normal
Dysmorphology	Normal
Indirect calorimetry	Normal
Glucose tolerance test	Normal
Auditory brainstem response	Normal
DEXA	Normal
Radiography	Normal
Body temperature	Normal
Eye morphology	Normal
Clinical chemistry	Normal
Plasma immunoglobulins	Normal
Haematology	Normal
Peripheral blood lymphocytes	Normal
Micronucleus test	Normal
Heart weight	Normal
Skin Histopathology	Normal
Brain histopathology	Normal
Salmonella infection	Normal
Citrobacter infection	Normal
All tests and analysis from

Model organisms have been used in the study of PNPT1 function. A conditional knockout mouse line, called Pnpt1^{tm1a(KOMP)Wtsi} was generated as part of the International Knockout Mouse Consortium program — a high-throughput mutagenesis project to generate and distribute animal models of disease to interested scientists.

Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion. Twenty six tests were carried out on mutant mice and two significant abnormalities were observed. No homozygous mutant embryos were identified during gestation, and therefore none survived until weaning. The remaining tests were carried out on heterozygous mutant adult mice; no additional significant abnormalities were observed in these animals.

Human PNPase I
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

External links

• Polynucleotide Phosphorylase at the US National Library of Medicine Medical Subject Headings (MeSH)