WB using Anti-Oct4 antibody shows detection of endogenous Oct4 in mouse embryonic fibroblast (MEF) cell lysate (lane 1) and HeLa nuclear extract (HN) (lane 2). The band at ~39 kDa (arrow head) corresponds to Oct4. After transfer, the membrane was blocked with 5% BSA. Primary antibody was used at a 1:1,000 dilution in PBS containing 5% BSA. The specificity of the antibody was confirmed by peptide competition which blocks reaction of the antibody with Oct4 (lanes 3 and 4, respectively).