Linking formins to Arp2/3

F-actin filaments can be induced to form by either of two pathways, but the elaborate cytoskeletal rearrangements seen in live cells imply that these mechanisms must somehow be coordinated. Now, Carnahan and Gould (page 851) provide the first evidence that a single, highly conserved protein links these two pathways during cytokinesis.

Previous work has shown that both the Arp2/3 complex and the formin family of proteins can induce F-actin nucleation, the rate-limiting step in filament formation. The authors show that in the yeast Schizosacchromyces pombe, the protein Cdc15p interacts directly with both the formin Cdc12p and an Arp2/3 complex regulator. Both Cdc12p and the Arp2/3 complex are essential for forming the cytokinetic actomyosin ring, a structure required for cell cleavage. The Cdc15p–Cdc12p complex appears in a medial structure in cells before ring...