The enzyme polynucleotide kinase (PNK, or ATP:5′-dephospho-polynucleotide 5′-phosphatase) catalyzes the transfer of a γ-phosphate group from a 5′-nucleoside triphosphate moiety to a free 5′-hydroxyl of a polynucleotide such as DNA or RNA, to form a 5′-phosphorylated DNA or RNA molecule and a nucleoside diphosphate.
