Jurkat cells were treated with 2 mM camptothecin for 6 hours. Cell lysate was prepared by homogenization in modified RIPA buffer (150 mM NaCl, 50 mM Tris-HCl, pH 7.4, 1 mM ethylenediaminetetraacetic acid, 1 mM phenylmethylsulfonyl flouride, 1% Triton X-100, 1% sodium deoxycholic acid, 0.1% sodium dodecylsulfate, 5 µg/ml of aprotinin, 5 µg/ml of leupeptin). Cell debris was removed by centrifugation. The cell lysate was then diluted to 1X SDS sample buffer (final concentration- 50 mM Tris-HCl, pH 6.8, 12.5% glycerol, 1% sodium dodecylsulfate, 0.01% bromophenol blue) containing 5% β-mercaptoethanol.