Regulates G protein-coupled receptor signaling cascades. Inhibits signal transduction by increasing the GTPase activity of G protein alpha subunits, thereby driving them into their inactive GDP- bound form. The RGS6/GNB5 dimer enhances GNAO1 GTPase activity (PubMed:10521509). . This is the function of RGS6 (regulator of G protein signaling 6, ENSG00000182732).