Granzyme A is a protein that in humans is encoded by the GZMA gene. Cytolytic T lymphocytes (CTL) and natural killer (NK) cells share the remarkable ability to recognize, bind, and lyse specific target cells. They are thought to protect their host by lysing cells bearing on their surface 'nonself' antigens, usually peptides or proteins resulting from infection by intracellular pathogens. The protein described here is a T cell- and natural killer cell-specific serine protease that may function as a common component necessary for lysis of target cells by cytotoxic T lymphocytes and natural killer cells. GZMA induces caspase-independent apoptosis in a characteristic manner, except it causes a distinctive form of DNA damage: single-stranded DNA nicking. A target of GZMA is the SET complex, including HMGB2 and ANP32A.