Spire (green) and Cappuccino (red) come together to nucleate actin.

Formins are thought both to extend existing actin filaments and to nucleate new ones. Work by Quinlan et al., however, reveals that one particular formin may not initiate new filaments but instead assist in a nucleation complex.

Actin nucleation and filament assembly are required for, among other things, cell polarity. This polarity fails in fly eggs when either Cappuccino (a type of formin) or Spire (a distinct actin nucleator) are missing. Both can nucleate filaments in vitro, and genetic and biochemical evidence suggest that the two work together to create polarity-inducing actin networks in vivo.

Quinlan et al. now show that Cappuccino and Spire proteins interact in vivo. But within this complex, only Spire seems to be capable of nucleation. When brought together with Spire, Cappuccino's nucleation ability was inhibited. Spire's nucleation activity, by...

The Rockefeller University Press
2007
The Rockefeller University Press
2007
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