Formin leaky cap allows elongation in the presence of tight capping proteins

Curr Biol. 2003 Oct 14;13(20):1820-3. doi: 10.1016/j.cub.2003.09.057.


Formins, characterized by formin homology domains FH1 and FH2, are required to assemble certain F-actin structures including actin cables, stress fibers, and the contractile ring. FH1FH2 in a recombinant fragment from a yeast formin (Bni1p) nucleates actin filaments in vitro. It also binds to the filament barbed end where it appears to act as a "leaky" capper, slowing both polymerization and depolymerization by approximately 50%. We now find that FH1FH2 competes with tight capping proteins (including gelsolin and heterodimeric capping protein) for the barbed end. We also find that FH1FH2 forms a tetramer. The observation that this formin protects an end from capping but still allows elongation confirms that it is a leaky capper. This is significant because a nucleator that protects a new barbed end from tight cappers will increase the duration of elongation and thus the total amount of F-actin. The ability of FH1FH2 to dimerize probably allows the formin to walk processively with the barbed end as the filament elongates.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actin Cytoskeleton / metabolism*
  • Chromatography
  • Chromatography, Gel
  • Dimerization
  • Microfilament Proteins / genetics*
  • Microfilament Proteins / metabolism*
  • Recombinant Fusion Proteins / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics*
  • Saccharomyces cerevisiae Proteins / metabolism


  • Bni1 protein, S cerevisiae
  • Microfilament Proteins
  • Recombinant Fusion Proteins
  • Saccharomyces cerevisiae Proteins