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. 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 independently of G-protein coupled receptors. In addition to its GEF activity, it plays an essential role in cortical subcellular localization of heterotrimeric G proteins, suggesting it acts as a facilitator of G-alpha function through control of its membrane targeting and/or assembling of associated components rather than a GEF (By similarity). Interacts with GDP-bound G(i)-alpha protein. Does not interact with G-alpha proteins when they are in complex with subunits beta and gamma. Localizes to the cell cortex. Belongs to the synembryn family.