A. HEK293T cells were transfected with expression constructs encoding MYC-FOXP3, His-Ubiquitin, and either a wild type or catalytically inactive (C282S, "cs") version of USP44 tagged with FLAG. Transfected cells were treated with 20 μM MG132 for 4 hrs and subsequently harvested for cell lysis. Pull-down of His-labeled proteins using Ni-NTA beads allowed recovery of ubiquitinated FOXP3 species that were then visualized by immunobot probing with antibodies specific for MYC. 