Ras-related Protein 1A (Rap1A) is a membrane-localized member of the Ras small GTPase superfamily of proteins. It is a 184 amino acid (aa) propeptide with a predicted molecular mass of 21 kDa. Bioactive Rap1A is processed into a 181 aa active form via the removal of aa 182-184. The rodent Rap1A orthologs share 100% aa identity with the human protein. The enzymatic activity of Rap1A is activated by EPAC and EPAC2, which are guanine nucleotide exchange factors (GEFs). Following activation, Rap1A interacts with PLCE1 and RADIL. Rap1A appears to play a vital role in the cardiovascular system where it regulates cell attachment, migration, and cell-cell junction formation. Rap1A counteracts the mitogenic functions of Ras, and several reports suggest that it mediates the progression of multiple cancers where it may regulate metastasis.