Down-regulates signaling from heterotrimeric G-proteins by increasing the GTPase activity of the alpha subunits, thereby driving them into their inactive GDP-bound form. Down-regulates G-protein-mediated release of inositol phosphates and activation of MAP kinases. Binds the GNB1-GNG2 heterodimer (By similarity). Binds EFNB1 and EFNB2. Long isoforms are cytoplasmic and associated with the plasma membrane. Short isoforms are nuclear. Detected in embryos from E8.5-16.5 in cortical ventricular zone, dorsal root ganglia and cerebellar primordia. Isoform 3 is detected in testis and in spermatocytes from newborn mice. Levels increase and reach a maximum after 21 days; after this they decrease again. Long isoforms are widely expressed. Phosphorylated by cyclic GMP-dependent protein kinase. ISGylated. Nuclear.