Rap1 signalling: Adhering to new models

Ras-like GTPases are ubiquitously expressed, evolutionarily conserved molec ular switches that couple extracellular signals to various cellular respons es. Rap1, the closest relative of Ras, has attracted much attention because of the possibility that it regulates Ras-mediated signalling. Rap1 is acti vated by extracellular signals through several regulatory proteins, and it might function in diverse processes, ranging from modulation of growth and differentiation to secretion, integrin-mediated cell adhesion and morphogen esis.