Characterization of GFR, a novel guanine nucleotide exchange factor for Rap1

Three groups of Rap1-specific guanine nucleotide exchange factors including C3G, CalDAG-GEFI, and Epac/cAMP-GEFI/II have been identified to date. In t he present study, me report a nem Rap1 guanine nucleotide exchange factor w hich me have named GFR (guanine nucleotide exchange factor for Rap1), GFR s hows close sequence similarity to EPAC/ cAMP-GEFI/II although GFR lacks a c AMP binding domain and contains a nuclear localization signal. We demonstra ted that GFR can activate Rap1 but not H-Ras in 293T cells and that the cdc 25 domain of GFR is required for the activation of Rap1, Northern blot anal ysis suggested that GFR mRNA is strongly expressed in the brain. In transfe cted HeLa cells, GFR has been found to be localized in the nuclei. (C) 1999 Federation of European Biochemical Societies.