RAPGEF5 acts as a guanine nucleotide exchange factor (GEF) for RAP1A, RAP2A and MRAS (M-Ras) in its GTP-bound form. Members of the RAS subfamily of GTPases function in signal transduction as GTP/GDP-regulated switches, cycling between an inactive GDP-bound state and an active GTP-bound state. GEFs such as RAPGEF5 promote the acquisition of GTP and so maintain the active state, forming a key link between cell surface receptors and RAS activation.

The UniProt annotation also notes that the association of RAPGEF5 with MRAS inhibits Rap1 activation, indicating that this protein can influence the balance of signalling between related small GTPases rather than simply switching them on. UniProt records the protein in the nucleus. The human RAPGEF5 gene is the source of the protein, and orthologous genes named Rapgef5 are recognised in mouse and rat, which allows comparative work in rodent models.

The gene has been known by several names: KIAA0277, GFR and MR-GEF, and the HGNC previous name was Rap guanine nucleotide exchange factor (GEF) 5. HGNC places it in the DEP domain containing gene group. Researchers studying RAPGEF5 are generally interested in how GEF activity towards Rap and M-Ras proteins is regulated and how it connects receptor signals to small GTPase pathways.