sentences:  In the dimeric holoenzyme, this subunit binds unprenylated Rab GTPases and then presents them to the catalytic Rab GGTase subunit for the geranylgeranyl transfer reaction.Rab GTPases need to be on either one or two cysteine residues in their C-terminus to localize to the correct intracellular membrane.CHM (gene) has been shown to interact with RAB1A, RAB7A and RAB3A.