Fig. 1. Schematic diagram of constructs used in this study. (A) P2X receptors are thought to assemble as homo- or hetero-trimers. Extracellular domains are not shown to aid visualization. (B) A single P2X4 subunit has intracellular N- and C-termini and two transmembrane domains. The position of epitope AU5 at residue 76 is shown as a blue circle. Diagrams of CD8 chimeras, CD8 (left), CD8-4C (middle) and CD8-4C (right). (C) Primary sequences of the C-termini of the constructs shown in B. (D) Sequence alignment of C-terminal regions of P2X subunits 1-6 from Rattus norvegicus, full or partially conserved residues are shown in bold. Total number of residues of each subunit is shown to the right, P2X2 and P2X5 have been truncated. Transmembrane helices in C and D are indicated by underlined regions. P2X4 is the only P2X family member that has a YXXG motif in its C-terminus. Other receptors and channels with a YXXG motif include the inward rectifier K⁺ channel Kir2.3, the adenosine receptor A2a and the cannabinoid receptor CB-2 (Royle et al., 2002).