A new regulatory protein that affects the state of actin polymerization.

A new protein factor that regulates the state of actin polymerization was purified from porcine brain by DNase I-agarose chromatography. The purified protein factor consisted of a 1 : 1 complex of 88,000 dalton polypeptide and actin. When actin was polymerized by salt in the presence of the factor, the steady-state viscosity and the sedimentability were greatly reduced. The extent of the reductions was found to be greater in the presence of Ca2+ than in its absence.