The RING domain is required for the effect of POSH. A, diagram shows a schematic structure of POSH. R, RING domain; SH, SH3 domain. The number above or below the corresponding domain indicates the deletion of amino acids in the constructs tested. B, effect of POSH and the truncated POSH on potassium current in oocytes injected with ROMK1 (R1), R1+POSH, and R1+truncated POSH. An asterisk indicates a significant difference in comparison with the control value (no POSH). **, p < 0.01; *, p < 0.05. The number in parentheses under each bar is the experimental number for each group. C, a Western blot demonstrating the association of ROMK1 and POSH or truncated POSH. IP, immunoprecipitation; IB, immunoblot.