Abstract Inward rectifying potassium (K + in) channels play an important role in turgor regulation and ion uptake in higher plants. Here, we report a previously unrecognized feature of these proteins: K + in channel C-terminal polypeptides mediate channel protein interactions. Using a C-terminal fragment of potato guard cell K + in channel KST1 in a yeast two-hybrid screen two novel putative K + in channel proteins (SKT2 and SKT3) were identified by interaction of their C-termini which contained a conserved domain (K HA). Interactions were confirmed by Western blot-related assays utilizing K + in channel C-termini fused to green fluorescence protein. Although deletion of the K HA-domain abolished these interactions, K + in currents were still detectable by patch-clamp measurements of insect cells expressing these KST1 mutants, indicating that formation of a functional channel does not depend on this C-terminal domain.