Apoptotic peptidase activating factor 1, also known as APAF1, is a protein which in humans is encoded by the APAF1 gene. This gene is mapped to chromosome 12q23. It encodes a cytoplasmic protein that initiates apoptosis. And it is an essential downstream effector of p53-mediated apoptosis. This protein contains several copies of the WD40 repeat domain, a caspase recruitment domain (CARD), and an ATPase domain (NB-ARC). In the presence of cytochrome c and dATP, APAF1 assembles into an oligomeric apoptosome, which is responsible for activation of procaspase-9 and maintenance of the enzymatic activity of processed caspase-9. Furthermore, APAF1 is inactivated in metastatic melanomas, leading to defects in the execution of apoptotic cell death. Additionally, APAF1 has been shown to interact with NLRP1, Caspase-9, APIP, BCL2-like 1 and HSPA4.