The chloride-bicarbonate exchanger AE1 is well characterized at one of its two major sites of expression, the red cell membrane (eAE1), where a number of important cytoskeletal interactions have been reported. In the kidney, requirements for its activity and regulation are somewhat different, since its major location is basolaterally in polarized epithelial cells (kAE1). Additionally, the N-terminus of kAE1 is significantly shorter than that of eAE1, so a number of cytoskeletal binding motifs are absent. Mutations in AE1 are associated with aan autosomal dominant human acidotic phenotype characterized by abnormal AE1 targeting. We have examined the C-terminal tail of AE1 (AE1C) for protein-protein interactions and identified several, including GAPDH. This is a necessary participant in basolateral localization as shown by siRNA knockdown experiments. The interaction holds true for AE2 and GAPDH in the liver. In addition, alterations in the PDZ-binding configuration of AE1C are associated with abnormal membrane residency, with one point mutation conferring a novel apical targeting signal.