Shaker family domains and regions that influence 3:1R and 2:2R heterotetramer formation. (A) The self-incompatible T1 hypothesis. T1 domains from Kv2-related regulatory subunits (Kv5.1, Kv6.1–6.4, Kv8.1–8.2 and Kv9.1–9.3) are hypothesized to be self-incompatible because they do not exit the ER and traffic to the cell surface. The cartoon shows (boxed) the potential Kv2 heterotetramers that could form based on the self-incompatible T1 hypothesis. (B) S6 consensus sequence logos generated by Pisupati et al. (2018) for Shaker-like Kv family subunits that form functional homotetrameric channels and the Kv2-related regulatory subunits from mouse Kv6, Kv8, and Kv9 subunits.