Human Son of sevenless homolog 1 (SOS1), also known as guanine nucleotide exchange factor 1 (GEF1), encompassing amino acids 594-1049. This construct contains an N-terminal FLAG-tag and a C-terminal Avi-tag™. The recombinant protein was affinity purified and enzymatically biotinylated using Avi-Tag™ technology. Biotinylation is confirmed to be ≥90%.