SOS1 (SOS Ras/Rac guanine nucleotide exchange factor 1) functions as a critical guanine nucleotide exchange factor that activates RAS signaling by promoting the exchange of GDP for GTP on RAS proteins 1. The protein serves as a key component in receptor tyrosine kinase signaling cascades, where it forms complexes with GRB2 to locally concentrate RAS activation 2. SOS1 operates through catalytic domain interactions with KRAS and can function in both membrane-bound and membraneless cytoplasmic protein granule contexts 21. The protein is subject to autoinhibition mechanisms that can be disrupted by pathogenic mutations 3. Clinically, SOS1 mutations cause Noonan syndrome, accounting for a significant portion of cases and typically presenting with distinctive phenotypes including high frequency of ectodermal anomalies, low prevalence of cognitive impairment, and cardiac defects 34. In cancer contexts, SOS1 represents an attractive therapeutic target as it serves as a feedback node in KRAS-driven tumors, with SOS1 inhibitors like BI-3406 showing efficacy when combined with MEK inhibitors 15. The protein's dual role in developmental disorders and cancer highlights its fundamental importance in cellular signaling regulation.