PNK (polynucleotide kinase) is a DNA repair enzyme that participates in single strand break repair and non-homologous end rejoining (NHEJ) for double strand breaks. PNK possesses a 5'-DNA kinase activity and a 3'-DNA phosphatase activity. It has three domains, a C terminal kinase domain, a central phosphatase domain, and an N-terminal forkhead associated (FHA) domain that is responsible for protein protein interactions. Reduction in expression of PNK by RNAi sensitizes cells to ionizing radiation and topoisomerase I inhibitors.
