Guanine nucleotide exchange factor (GEF), which can activate some, but not all, G-alpha proteins independently of G-protein coupled receptors. Acts by exchanging bound GDP for free GTP. Also able to activate the G(s)-alpha in synaptic signaling network. Plays a key role in asymmetric spindle positioning, a step for asymmetric cell division that generates cell diversity during development by activating G(i) alpha protein goa-1 and gpa-16 independently of G-protein coupled receptors (By similarity). Localizes to the cell cortex. Belongs to the synembryn family.