Subunit of glucosidase 2, which cleaves sequentially the 2 innermost alpha-1,3-linked glucose residues from the Glc(2)Man(9)GlcNAc(2) oligosaccharide precursor of immature glycoproteins. Specifically required for the cleavage of the final glucose. Heterodimer of a catalytic subunit alpha (ROT2) and a subunit beta (GTB1). Present with 9760 molecules/cell in log phase SD medium.