C. Levels of polyubiquitinated FOXP3 in the presence or absence of USP44. As in Fig 2b, murine iTregs were generated from naïve CD4+ precursors isolated from wild type and mice globally deficient in USP44-/- mice (n=3/group/experiment). Ubiquitinated proteins were extracted from iTreg lysates with anti-ubiquitin antibodies (anti-Ubi) prior to resolution by SDS PAGE and immunoblot analysis, probing for FOXP3. 