Western blotting with the MUM1p monoclonal antibody. (A) A band of ∼50-kd of the expected size of MUM1-myc protein is seen in the line corresponding to pCEP4-MUM1-myc HeLa-transfected cells (HeLa-MUM1) but not in negative control HeLa cells. Tubulin levels are shown below as control for the amount of the loaded protein. (B) A 50-kd band of the expected molecular size of the MUM1 protein is seen in lanes 2 and 4, corresponding to the IM9 myeloma cell line and normal tonsil. No bands are detected in lanes 1 and 3, corresponding to U937 and HeLa cell lines. Identical results (not shown) were obtained with the monoclonal (clone MUM97) and polyclonal anti-IRF4/ICSAT antibody. In both experiments, β-tubulin levels are shown below to control for the integrity and amount of the loaded protein.