Enables guanyl-nucleotide exchange factor activity. Acts upstream of or within several processes, including B cell homeostasis; regulation of T cell activation; and regulation of pro-B cell differentiation. Is expressed in several structures, including genitourinary system; hemolymphoid system gland; intestine; liver; and lung. Human ortholog(s) of this gene implicated in Noonan syndrome 9. Orthologous to human SOS2 (SOS Ras/Rho guanine nucleotide exchange factor 2). [provided by Alliance of Genome Resources, Apr 2022]