Guanine nucleotide exchange factor (GEF), which can activate some, but not all, G-alpha proteins 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.