 The CDC25 homology domain, also called the RasGEF domain, is the catalytic domain of many Ras GEFs, which activate Ras GTPases.The CDC25 domain comprises approximately 500 amino acids and was first identified in the CDC25 protein in budding yeast "Saccharomyces cerevisiae".Dbl-like RhoGEFs were present at the origin of eukaryotes and evolved as highly adaptive cell signaling mediators.