This protein consists of G monomers which polymerize into F filaments, which make up the microfilaments of the cytoskeleton.  
One protein that binds to this protein also binds to proline-rich sequences in the membrane proteins Vasp and Mena, and another is knocked out in the singed mutant.  Phosphatidyl-inositol-4,5-bisphosphate regulates the binding of vinculin to both talin and this other protein, whose function is performed by nematode Major Sperm Protein in the only (*) eukaryotic cells known to lack one form of it.  In addition to the aforementioned profilin and facsin, severin and gelsolin bind to this protein and sever it.  Two toxins often used to study it are cytochalasins and phalloidin.   Thymosin β4 sequesters this protein, which undergoes treadmilling because the critical concentration at its (+) and (-) ends is not the same.  This protein consists of G monomers which polymerize into F filaments, which make up the microfilaments of the cytoskeleton.  For 10 points, name this protein that forms cross-bridges with myosin in muscle cells.
One protein that binds to this protein also binds to proline-rich sequences in the membrane proteins Vasp and Mena, and another is knocked out in the singed mutant.  
{actin} (2) [DW]