Tying the knot: linking cytokinesis to the nuclear cycle

For the survival of both the parent and the progeny, it is imperative that the process of their physical division (cytokinesis) be precisely coordinat ed with progression through the mitotic cell cycle. Recent studies in the b udding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharom yces pombe are beginning to unravel the nature of the links between cytokin esis and the nuclear division cycle. The cyclin-dependent kinases and a nov el surveillance mechanism that monitors cytokinesis and/or morphogenesis ap pear to play important regulatory roles in forging these links. It is becom ing increasingly clear that the inactivation of the mitosis-promoting cycli n-dependent kinase, which marks the completion of the nuclear division cycl e, is essential for actomyosin ring constriction and division septum assemb ly in both yeasts. Additionally, the spindle pole bodies are emerging as im portant transient locale for proteins that might play a key role in couplin g the completion of mitosis to the onset of cytokinesis.