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

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