T4 Polynucleotide Kinase catalyzes the phosphorylation of 5′ hydroxyl termini of double- and single-straned DNA or RNA. Catalyzes the transfer of the γ-phosphate of ATP to a 5′-OH terminus in DNA or RNA. Contains 3′-phosphatase activity. T4 Polynucleotide Kinase is used for 5′-end labeling of nucleic acids prior to DNA or RNA sequencing. The enzyme phosphorylates synthetic linkers and fragments of DNA or RNA prior to ligation. Labels 5′-termini prior to partial restriction enzyme digestion.