Ras protein signalling

Ras proteins were identified through their association with cell transforma tion. Since then they have been shown to regulate cell growth, differentiat ion and apoptosis, as well as influencing processes such as cell migration and neuronal activity. Ras regulates a number of signalling molecules by tr anslocating them to the plasma membrane for activation. An emerging concept is that Ras acts as a branchpoint in signal transduction because it orches trates the activity of multiple signalling pathways to regulate diverse cel lular functions. This implies a degree of selectivity in the ability of Ras to activate particular arms of each pathway, but the mechanisms by which t his is achieved are not known. Ras is also an important regulator of immune function and in this review, we summarise current understanding of Ras reg ulation and function and discuss some new aspects of Ras signalling where u nderstanding is less clear.