The noose tightens

Abstract

As endosymbiotic interlopers, mitochondria and chloroplasts must intimately coordinate their activities with the nuclear — cytoplasmic system in which they dwell. Among these, accomplishing organellar divisions and keeping them in step with the host's mitotic cycle pose central problems. Chloroplasts have retained the division apparatus of their prokaryotic progenitors; they employ homologs of the bacterial cell division GTPase FtsZ to form rings that constrict the inner and outer envelope membranes as the organelle divides. Although an algal species appears to use a FtsZ-like protein to cleave its mitochondria, the Saccharomyces cerevisiae and Caenorhabditis elegans genomes lack good candidates for FtsZ homologs. Rather, recent work demonstrates that for this task fungi and animals have co-opted proteins similar to dynamin, the GTPase located in the constricting ring that pinches off coated vesicles as they form at the plasma membrane. Now, three groups 1–3 have converged on crucial components of the protein machinery that mediates mitochondrial division in yeast.