PRAF3, which is the PRA1-superfamily member, plays important roles in membrane traffic as a GDI displacement factor via physical interaction with a variety of Rab proteins, as well as in the modulation of antioxidant glutathione through its interaction with EAAC1 (SLC1A1).  It is known that the overexpression of PRAF3 induces the toxicity of the host cell, however, the factors capable of cancelling the toxicity remained unknown.  Our findings demonstrate that one of Rab proteins can relieve the cytotoxicity of PRAF3 both in yeast and a human cell expression system.  The ability of Rab protein to cancel the toxicity could further imply that PRAF3 and Rab proteins are closely related to each other physiologically and genetically.