XAB1, as known as GPN1, belongs to the GPN-loop GTPase family. Small GTPases share a biochemical mechanism and act as binary molecular switches. One important function of small GTPases in the cell is nucleocytoplasmic transport of both proteins and RNA. This protein may play a role in DNA repair and may function in activation of transcription. And it forms an interface between the RNA polymerase II enzyme and chaperone/scaffolding protein, suggesting that it is required to connect RNA polymerase II to regulators of protein complex formation. Recombinant human XAB1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.