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 ligation reactions.

This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with an alcohol group as an 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.

• 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. doi:10.1016/S0021-9258(18)96553-1. 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. doi:10.1016/S0021-9258(18)96554-3. PMID 4287930.

• Vivo
• New England Biolabs' T4 PNK page