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Nat Cell Biol. 2002 Aug;4(8):626-31.

An actin nucleation mechanism mediated by Bni1 and profilin.

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Department of Pediatric Oncology, The Dana-Farber Cancer Institute Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA.


Formins are required for cell polarization and cytokinesis, but do not have a defined biochemical activity. In Saccharomyces cerevisiae, formins and the actin-monomer-binding protein profilin are specifically required to assemble linear actin structures called 'actin cables'. These structures seem to be assembled independently of the Arp2/3 complex, the only well characterized cellular mediator of actin nucleation. Here, an activated yeast formin was purified and found to promote the nucleation of actin filaments in vitro. Formin-dependent actin nucleation was stimulated by profilin. Thus, formin and profilin mediate actin nucleation by an Arp2/3-independent mechanism. These findings suggest that distinct actin nucleation mechanisms may underlie the assembly of different actin cytoskeletal structures.

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