Four TRP proteins are required to form a tetrameric complex which functions as an ion channel. The domain for channel assembly has been localised in different TRP channels to the N-terminus, e.g. ankyrin-like repeats (ANKR) are essential for TRPV4,5 and 6 multimerisation, or the coiled-coiled region for TRPC1. TRPC4 and TRPC5 have been shown to form both homo and heteromeric channels where both channel types exhibit two ANKR and a coiled-coiled region in their N-terminus. We used both N- and C-terminal fragments of either TRPC4 or TRPC5 and coexpressed these fragments with full length TRPC4 or TRPC5 protein. Whole-cell currents, using the patch clamp technique, showed that fragments which include the first ANKR potently down-regulate TRPC4 and TRPC5 currents, whereas other fragments had no dominant-negative effect. In accordance, confocal FRET microscopy revealed strongest interaction for YFP/CFP-tagged fragments that include the first ANKR. Additionally, a mutant lacking the first ANKR failed to form multimers, lacked ion-channel function and remained predominantly intracellular. We conclude that the first ANKR in TRPC4 and TRPC5 is essential for the formation to both homo-and heteromultimeric channels. Supported by Austrian Science Foundation FWF-16387, FWF-15387.