Polynucleotide 5'-hydroxyl-kinase
      
In enzymology, a polynucleotide 5'-hydroxyl-kinase (EC 2.7.1.78) is an enzyme that catalyzes the chemical reaction
- ATP + 5'-dephospho-DNA 
 ADP + 5'-phospho-DNA 
Thus, the two substrates of this enzyme are ATP and 5'-dephospho-DNA, whereas its two products are ADP and 5'-phospho-DNA. Polynucleotide kinase is a T7 bacteriophage (or T4  bacteriophage) enzyme that catalyzes the transfer of a gamma-phosphate from ATP to the free hydroxyl end of the 5' DNA or RNA. The resulting product could be used to end-label DNA or RNA, or in a ligation reaction.
 Nomenclature 
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with an alcohol group as acceptor.  The systematic name of this enzyme class is ATP:5'-dephosphopolynucleotide 5'-phosphotransferase. Other names in common use include:
- ATP:5'-dephosphopolynucleotide 5'-phosphatase
 
-  PNK
 
-  polynucleotide 5'-hydroxyl kinase (phosphorylating),
 
-  5'-hydroxyl polynucleotide kinase,
 
-  5'-hydroxyl polyribonucleotide kinase,
 
-  5'-hydroxyl RNA kinase,
 
-  DNA 5'-hydroxyl kinase,
 
-  DNA kinase,
 
-  polynucleotide kinase, and
 
-  polynucleotide 5'-hydroxy-kinase.  
 
References
-  Novogrodsky A, Hurwitz J (1966). "The enzymatic phosphorylation of ribonucleic acid and deoxyribonucleic acid. I. Phosphorylation at 5'-hydroxyl termini". J. Biol. Chem. 241 (12): 2923–32. PMID 4287929. 
 
-  Novogrodsky A, Tal M, Traub A, Hurwitz J (1966). "The enzymatic phosphorylation of ribonucleic acid and deoxyribonucleic acid. II. Further properties of the 5'-hydroxyl polynucleotide kinase". J. Biol. Chem. 241 (12): 2933–43. PMID 4287930. 
 
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