Two kinds of BIR-containing protein - inhibitors of apoptosis, or requiredfor mitosis

The baculoviral IAP repeat (BIR) is a zinc-binding fold. Some BIR-containin g proteins (BIRCs), including several from insect viruses, insects and vert ebrates, are inhibitors of cell death and act by binding to active caspases , Their ability to do so can be antagonized by pro-apoptotic insect protein s such as Grim, HID and Reaper, or the mammalian protein Diabio/Smac. Membe rs of one structurally distinct subgroup of BIR-containing proteins, which are present in yeasts and Caenorhabditis elegans as well as insects and ver tebrates, do not act as caspase inhibitors; instead, they are required for chromosome segregation and cytokinesis, and act in concert with inner centr omere protein (INCENP) homologues and aurora kinase homologues.