Western blot analysis of RFC expression in CCRF-CEM cells and their PT523-resistant sublines. Microsomes were isolated from exponentially growing cells and proteins were extracted using a Triton X-100-containing buffer as detailed in “Materials and methods.” Aliquots of microsomal proteins (75 μg) from RFC overxepressing CEM-7A cells, WT cells, and their PT523-resistant sublines were resolved by electrophoresis on 10% polyacrylamide gels containing SDS and electroblotted onto a Nytran nylon membrane (Schleicher and Schuell). Then, the blots were reacted with a peptide antiserum against a C-terminal peptide of human RFC⁹  and detected by enhanced chemiluminescence (A). An internal 148-kDa protein detected during the Panceau S staining was used to normalize for any differences in protein loading (B).