DNA-protein kinase catalytic subunit (DNA-PKcs) also known as DNA-activated kinase is a nuclear 460-470 kD serine threonine kinase involved in double-stranded DNA break repair, VDJ recombination, and transcriptional modulation. DNA-PKcs must bind DNA ends to become active. DNA-PKcs is modified by phosphorylation and has been shown to interact with Ku70/Ku80, KIP, DNA-ligase IV, and XRCC4 proteins. The 7A4 monoclonal antibody has recognizes human DNA-PKcs and has been shown to be useful for immunofluorescence staining and Western blotting.