Immunoblot analysis of NPM-ALK protein expressed in mouse lymphomas. Lane 1 contains protein extracts from the human T-cell leukemia line CEM, which does not contain the t(2; 5), whereas lane 2 contains extracts from the t(2; 5)-positive lymphoma line SUP-M2. Lane 3 contains protein extracts from the liver of a normal BALB/cByJ mouse, whereas lanes 4 and 5 contain proteins prepared from mesenteric node or subcapsular renal tumors, respectively, from mouse GT4. The arrow indicates the position of the 75-kD NPM-ALK fusion protein. The smaller immunoreactive bands present in lane 4 probably represent partial proteolytic degradation of the NPM-ALK protein in the tumor sample.