UASp regulatory sequences drive expression of amino acids 1-18 of Tak1, followed by amino acids 128-385 of slpr and 272-678 of Tak1. Three residues in the slpr activation loop have been mutated to alanine to prevent activating phosphorylation (T287A, S291A and T295A). The construct is tagged at the C-terminal end with two copies of Tag:HA.