Fig. 2.

Homeostasis between G-actin and F-actin. In typical cultured cells, conversion between monomeric ‘G-actin’ and filamentous ‘F-actin’ occurs in every a half to a few minutes. G-actin and F-actin exist roughly at the 1:1 ratio. G-actin sequestering proteins bind G-actin and prevent uncontrolled actin nucleation by lowering the concentration of ‘free’ G-actin. The concentration of total G-actin may exceed 100 μM while the concentration of free G-actin is kept low at a range of 0.1–1 μM.^9),170) Because of the large size of the G-actin pool, little has been investigated about the role of the G-actin pool in actin remodeling. However, my two independently-developed researches have converged into an intriguing finding that the actin disassembly and F-actin nucleation activities are tightly coupled in times and places within the cell.⁹⁾