CELLULAR-RESPONSES REGULATED BY RHO-RELATED SMALL GTP-BINDING PROTEINS

Rho-related proteins are members of the ras superfamily of small GTP-b inding proteins. Their function in fibroblasts has been analysed using microinjection of living cells. Rho appears to link plasma membrane r eceptors to the assembly of focal adhesions and actin stress fibres. T he closely related protein rac, on the other hand, links receptors to the polymerization of actin at the plasma membrane to form membrane ru ffles and pinocytotic vesicles. In phagocytic cells, rac has been show n to be required for activation of a membrane-bound NADPH oxidase in r esponse to receptor activation. These systems provide the basis for a working model for the mechanism of action of the rho family of small G TPases.