Fig. 4. Ion channel clustering requires interaction of PSD-95 with a tetrameric ion channel. (A,B) PSD-95 forms clusters when co-transfected with K⁺ channel Kv1.4. (C,D) A tandem construct containing four covalently linked Kv1.4 subunits does not form clusters with PSD-95. (E,F) A monomeric transmembrane protein containing a C-terminal PDZ binding site (Tac-SDV) does not cluster when simply co-transfected with PSD-95. (G,H) However, this Tac-SDV construct is recruited to clusters when co-transfected with PSD-95 and Kv1.4. (I,J) This co-clustering requires the PDZ binding site on Tac, as the native Tac construct remains diffuse in cells containing PSD-95/Kv1.4 clusters. Bar, 10 µm.