Role for yeast inhibitor of apoptosis (IAP)-like proteins in cell division

Inhibitors of apoptosis (IAPs) are a family of proteins that bear baculovir al IAP repeats (BIRs) and regulate apoptosis in vertebrates and Drosophila melanogaster. The yeasts Saccharomyces cerevisiae and Schizosaccharomyces p ombe both encode a single IAP, designated BIR1 and bir1, respectively, each of which bears two BIRs. In rich medium, BIR1 mutant S,cerevisiae underwen t normal vegetative growth and mitosis. Under starvation conditions, howeve r, BIR1 mutant diploids formed spores inefficiently, instead undergoing pse udohyphal differentiation Most spores that did form failed to survive beyon d two divisions after germination. bir1 mutant S. pombe spores also died in the early divisions after spore germination and became blocked at the meta phase/anaphase transition because of an inability to elongate their mitotic spindle, Rather than inhibiting caspase-mediated cell death, yeast IAP pro teins have roles in cell division and appear to act in a similar way to the IAPs from Caenorhabditis elegans and the mammalian IAP Survivin.