Cleavage reaction of MDR1 mRNA with ribozymes. Ribonuclease protection assay was performed to study for the cleavage of MDR1 mRNA by the ribozyme expressed in MOLT-3/TMQ 800 cells. Lane 1, probe only; lane 2, probe hybridized with yeast tRNA, digested with ribonucleases; lane 3, protected fragment of MDR1 mRNA; lane 4, 1 μg of mRNA extracted from MOLT-3/TMQ 800 cells plus 179 MDR1 ribozyme; lane 5, 1 μg of mRNA extracted from MOLT-3/TMQ 800 cells plus 196 MDR1 ribozyme.