Small GTPases are a super-family of cellular signaling regulators. Rap family members (Rap1A, Rap1B, Rap2A, Rap2B, and Rap2C) are Ras-like GTPases that regulate cell proliferation, differentiation, apoptosis and adhesion mechanisms. Rap1 (Ras-proximate-1) regulates apoptosis through interaction with two MAP3K effectors of the MEK/ERK MAP-kinase pathway, Raf-1 and B-Raf. Rap1 regulates cell adhesion mechanisms through effector molecules such as the integrins and cadherins.