Guanine nucleotide exchange factor (GEF), which can activate some, but not all, G-alpha proteins. Able to activate GNAI1, GNAO1 and GNAQ, but not GNAS by exchanging bound GDP for free GTP. Involved in regulation of microtubule pulling forces during mitotic movement of chromosomes by stimulating G(i)-alpha protein (By similarity). Interacts with some GDP-bound G alpha proteins. Does not interact with G-alpha proteins when they are in complex with subunits beta and gamma (By similarity). Belongs to the synembryn family.