Rap GTP-binding protein also known as Ras-related proteins or simply RAP is a type of small GTPase, similar in structure to Ras.
These proteins share approximately 50% amino acid identity with the classical RAS proteins and have numerous structural features in common. The most striking difference between RAP proteins and RAS proteins resides in their 61st amino acid: glutamine in RAS is replaced by threonine in RAP proteins. RAP counteracts the mitogenic function of RAS because it can interact with RAS GAPs and RAF in a competitive manner.
^Rousseau-Merck MF, Pizon V, Tavitian A, Berger R (1990). "Chromosome mapping of the human RAS-related RAP1A, RAP1B, and RAP2 genes to chromosomes 1p12----p13, 12q14, and 13q34, respectively". Cytogenet. Cell Genet.53 (1): 2–4. doi:10.1159/000132883. PMID2108841.