Ras is a small GTP-binding protein involved in many cellular processes, including proliferation, differentiation and apoptosis. Ras transmits signals of cell surface receptors by binding to a variety of effector molecules. In addition to the well-characterized effectors Raf and PI-3 kinase, Ras also interacts with a group of homologous, noncatalytic proteins composed of RASSF1, RASSF2, RASSF3, AD037 and Nore1. RASSF1 is a potential tumor suppressor gene that plays an important role in tumor pathogenesis. Nore1 binds to Ras in response to EGF or serum stimulation, but its function has yet to be determined. RASSF2 is a nuclear protein containing a Ras-associating domain and a SARAH domain. RASSF2 isoform A is inactivated in colorectal cancer cells by CpG island promoter hypermethylation.