Son of Sevenless Homolog 2 (SOS2) is one of two SOS family proteins. SOS proteins act as guanine nucleotide exchange factors for Ras. Human SOS2 is a 1332 amino acid (aa) protein with a predicted molecular mass of 153 kDa. The mouse SOS2 ortholog shares 95% aa sequence identity with the human protein. It is widely expressed and acts downstream of multiple receptor tyrosine kinases, cytokine receptors, and G protein-coupled receptors to activate Ras. SOS2 shares 70% aa identity with SOS1. However, unlike SOS1, which supports both short-term and long-term Ras activation, SOS2 initiates only short-term Ras activation. While SOS1 is required during embryonic development, SOS2 is dispensable for mouse development and growth as SOS2 knockout mice are viable.