| Therefore C termini of Kir2 . 1 ( + ) , Kir2 . 3 ( + ) , Kir2 . 4 ( ) , Kir3 . 1 ( ) , Kir3 . 2 ( + ) , Kir3 . 3 ( + ) and Kir3 . 4 ( ) subunits ( + , motif present ; , motif absent ) were used as baits in the yeast two hybrid assay to screen for in vivo interaction with PDZ domains 1 3 of PSD 95 / SAP90 . ^^^ In contrast to Kir2 . 1 and Kir2 . 3 , all Kir 3 fragments failed to bind PSD 95 in this assay , which was supported by the lack of coimmunoprecipitation and colocalization of the entire proteins in mammalian cells . ^^^ Kir2 . 1 and Kir2 . 3 subunits on the other hand coprecipitate with PSD 95 . ^^^ When coexpressed in a bicistronic internal ribosome entry site expression vector in HEK 293 cells macroscopic and elementary current analysis revealed that PSD 95 suppressed the activity of Kir2 . 3 channels by > 50 % . ^^^ This inhibitory action of PSD 95 , which predominantly affects the single channel conductance , is likely attributable to a molecular association with additional internal interaction sites in the Kir2 . 3 protein . . ^^^ |