T4 Polynucleotide Kinase (NEB #M0201) can be used to 5' end label DNA and RNA because it catalyzes the transfer and exchange of phosphate from ATP to the 5´ -hydroxyl terminus of polynucleotides (double-and single-stranded DNA and RNA) and nucleoside 3´-monophosphates. Polynucleotide Kinase also catalyzes the removal of 3´-phosphoryl groups from 3´-phosphoryl polynucleotides, deoxynucleoside 3´-monophosphates and deoxynucleoside 3´-diphosphates (1). T4 Polynucleotide Kinase (3' phosphatase minus) (NEB #M0236) is a modified version that exhibits full kinase activity with no 3´ phosphatase activity (2,3). NEBCloner is a guide for selecting appropriate products and viewing protocols for steps in the cloning workflow. To help select the right kinase, choose "End Modification" on the tool to start. References Richardson, C.C. (1981) P.D. Boyer (Eds.), The Enzymes, 14, pp. 229-314. San Diego: Academic press. Wang, L.K. and Shuman, S. (2001) J. Biol. Chem., 276, 26868-26874. PMID: 11335730 Wang, L.K. and Shuman, S. (2002) Nucl. Acids Res., 30, 1073-1080. PMID: 11842120