Separation of nuclear and cytoplasmic proteins by differential centrifugation in non-ionic detergent. Panel A, B, C and D show fractionation results from HeLa, HCT116, HEK293 and Hs68 cells, respectively. The upper panel in each section shows immunoblotting results for nuclear markers (nucleoporin or lamin A) and the lower panels show the same for cytoplasmic markers (pyruvate kinase or tubulin). Subcellular fractions are abbreviated as W for whole cell lysate, C for cytoplasmic fraction and N for nuclear fraction. In panel A, HeLa cells were obtained from two independent culture dishes, and results are shown as W1, W2, C1, C2, N1 and N2.