Promotes the exchange of Ras-bound GDP by GTP. May also play a role in the activation of rasG. Expressed during development; especially between 8-18 hours of development. Expressed (at protein level). Phosphorylated on threonine residues. Absence of the phosphoprotein gefR. Was originally (PubMed:8793298) named RasGEFA, as it was the second RasGEF, after aimless, to be identified there. When aimless, aleA, was renamed gefA to make the nomenclature consistent and systematic, RasGEFA was renamed gefR.