Southern blot analysis of Ig and TCR gene rearrangements and retroviral integrations in tumors from transplant recipients with NPM-ALK–induced lymphomas. High molecular weight genomic DNA isolated from tissue samples was digested to completion with EcoRI (A, C, and D) or HindIII (B). In each panel, lane 1 contains DNA from the liver of a normal control mouse; lanes 2, 3, and 4 contain tumor DNA from animal GT2; lane 5 contains mesenteric tumor DNA from animal GT4; and lane 6 contains spleen tissue from animal GT4. The Southern blots were hybridized with murine probes for J_H (A), J_κ (B), TCRβ (C), and Alk (D). Size markers are shown to the left. Arrows indicate germline fragments. Low-level tumor cell involvement of the GT4 spleen is evident from the single proviral integration site identified (note the faint ∼6.5-kb fragment in [D], lane 6). The Alk cDNA probe is highly conserved with respect to the corresponding segment in the human NPM-ALK gene and thus cross-hybridizes with the restriction fragments representing sites of proviral integration.