Figure 1. Rho GTPase activity is tightly regulated to create distinct zones of activation.

a. Typical Rho family GTPases cycle between an active, GTP-bound state and an inactive, GDP-bound state. GEFs promote the active state by exchanging GDP for GTP, while GAPs inactivate GTPases by stimulating GTP hydrolysis. Rho GDI sequesters Rho-GDP in the cytoplasm, protecting it from degradation and preventing its activation. In the active conformation, Rho GTPases activate effectors through direct binding, usually by relieving an autoinhibited conformation, allowing them to act on their downstream targets.

b. RhoA is active in distinct zones in epithelia: at cell-cell junctions and at the contractile ring of dividing cells.