Beta subunit of both type II and type III geranylgeranyltransferase complexes; provides a prenylated membrane attachment moiety for Rab-like proteins Ypt1p and Sec4p as part of GGTase-II; functions with α subunit Ecm9p (GGTase-III) in the transfer of a geranylgeranyl group to mono-farnsylated Ykt6p, regulating membrane localization and function in cell wall integrity and autophagy; required for vesicular transport between the ER and Golgi; human homolog RabGGTB, can complement yeast BET2 mutants