| Description | Rap1 is a member of the Ras superfamily of monomeric GTPases, closely related to Ras. There are two isoforms, Rap1Aand Rap1B that share 95% identity and are encoded by two different genes. Rap1 proteins share 50% identity with Ras proteins, including the regions involved in GDP/GTP binding (hence Rap1A has very similar biochemical properties to Ras), C-terminal CAAX domain leading to prenylation (geranylgeranylation in the case of Rap1A), and effector region identical to that of Ras proteins causing Ras and Rap1 to share some potential effectors. |
| Expression | ubiquitous ; highest in platelets and neutrophils |
| Localisation | Rap1 is bound to membranes. In many cell types, it is found in a perinuclear compartment overlapping the Golgi. Rap1 proteins (A and B) are phosphorylated near the C-ter by cAMP-dependent protein kinase. This results in translocation of part of the Rap1 pool to the cytosol. |
| Function | The function of Rap1 is still a matter of debate. Its overexpression is able to compete with the activation of Raf-1 by active Ras. Active Rap1B has been shown to activate the B-Raf kinase and the MEK-ERK cascade. In several cellular models, Rap1 has been shown to be involved in the regulation of integrin-mediated cell adhesion. |
| Homology | 98% identical to Rap1A, 60% identical to Rap2 , 50 % to Ras proteins |
