45K ACTIN FILAMENT-SEVERING PROTEIN FROM SEA-URCHIN EGGS - INTERACTION WITH PHOSPHATIDYLINOSITOL-4,5-BISPHOSPHATE

An actin filament-severing activity of 45K protein isolated from sea u rchin eggs was abolished when this protein was incubated with phosphat idylinositol-4,5-bisphosphate (PIP2). This effect was specific to PIP2 since phosphatidylinositol, phosphatidylinositol-4-monophosphate, ino sitol-1,4,5-trisphosphate, and phosphatidylserine did not show such an effect at the same concentration. Digestion of PIP2 with phospholipas e C eliminated the effect. On the other hand, PIP2 did not affect eith er the formation of 45K protein-actin complex or actin filament-cappin g activity of the complex. Possible implication of the binding of PIP2 to 45K protein in cytoskeleton formation after fertilization of sea u rchin eggs is discussed.