In mammals, there exist two major isoforms, Rab GDI α (also known as XAP-4) and Rab GDI β. While the mammalian Rab GDI β-genes are ubiquitously expressed, the Rab GDI α genes are predominantly brain-specific. Since it is expressed predominantly in neural and sensory tissues, Rab GDI α may serve a specific function in neural signalmtransmission. The gene sequences for the Rab GDI proteins are extremely conserved in evolution, with substantial homology preserved across three eukaryotic kingdoms.
