Molecular genetics. A protein involved in enabling cells to respond to DNA damage. 53BP1 binds to the DNA-binding domain of p53 tumor suppressor and enhances p53-mediated transcriptional activation. 53BP1 and gamma‑H2AX are able to produce discrete DNA repair foci. Foci formation is a sensitive indicator to detect DNA damage, especially DNA-double strand breaks. Staining with specific antibodies shows the foci marking double-strand breaks. By repairing double-strand breaks the visible foci decrease.