The KLF4 N-terminus is critical for interaction with FBXO32. (a) Schematic of human KLF4 with functional domain, as well as deletion mutants generated in this study. AD, transactivation domain; ID, transrepression domain; NLS, nuclear localization signal; Z, zinc-finger domain. (b) Deletion of amino acids 1–60 stabilizes KLF4. Flag-tagged wild-type or deletion mutants of KLF4 were transfected into HEK293T cells together with empty vector or Myc-tagged FBXO32. Twenty-four hours after transfection, the protein level of wild-type KLF4 or deletion mutants were tested by immunoblotting with antibody against Flag. (c) Deletion of amino acids 1–60 eliminates KLF4 and FBXO32 interaction. Indicated plasmids were transfected into HEK293T cells. Twenty-four hours after transfection, the cells were treated with MG132 for 4 h. Co-IP was performed with anti-Flag M2 affinity gel.