Western analysis for PML/RAR expression in ribozyme-transfected NB4-R1 cells. NB4-R1 cells transfected with either the control ribozyme, APL 5.0, or the catalytic ribozyme, APL 1.1, were cultured in 65 or 195 μg/mL hygromycin (hygro) in the absence (−) or presence (+) of 10⁻⁶ mol/L ATRA for 5 days. Total cellular protein was extracted and analyzed by Western analysis, using an anti-RAR antibody to detect PML/RAR protein. Relative to APL 5.0 transfectants, this immunoblot indicates that a marked reduction of PML/RAR expression occurs in APL 1.1-transfected NB4-R1 cells, especially after ATRA treatment and selection at the 195 μg/mL hygromycin dosage.