Fig. 1. UBB⁺¹ is degraded by the UPS at low expression levels. (A,B) Western blot of cell lysates of HeLa cells transiently transfected with inducible Tet-off CMV-UBB⁺¹ vectors treated with decreasing Dox concentrations. UBB⁺¹ was detected with anti-UBB⁺¹ antibody (Ub3) (De Vrij et al., 2001) in cells without proteasome inhibitor treatment (A) or in cells treated overnight with 1 µM proteasome inhibitor MG132 (B). CMV-UBB⁺¹ pcDNA3 (UBB+1) and empty pcDNA3 vector (control) transfections served as controls. Arrows in B indicate additional UBB⁺¹ expression after proteasome inhibitor treatment. Protein input was equal in all lanes as determined by Bradford protein measurement (not shown); this is a representative experiment of two duplicate experiments. Molecular mass in kDa is indicated on the left. ^*UBB⁺¹; ^**Ub-UBB⁺¹.