UPK3B is a minor component of the apical plaques of mammalian urothelium that binds and dimerizes with uroplakin-1b (UPK1B，MIM 602380)，one of the major conserved urothelium membrane proteins. The other major conserved integral membrane proteins of urothelial plaques are UPK1A (MIM 611557)，UPK2 (MIM 611558)，and UPK3A (MIM 611559)
