Southern blot of PML-RARα + MYC leukemias shows clonal retroviral integrations. Genomic DNA samples were digested with EcoRI, which cuts within the multicloning site of retroviral integrants, and the blot was probed with a probe hybridizing to GFP sequences. 6989, A GFP⁺ leukemia that arose in a PML-RARα + MIG recipient mouse. 34, A GFP⁺ lymphoblastic lymphoma that arose in a recipient of Control + MYC-transduced bone marrow. PR+MYC Pre, preleukemic bone marrow from PML-RARα + MYC mice 5 wk after transplantation. PR+MYC, PR+MYC^ΔMBII, and PR+MYC^T58A, leukemias that arose from recipients of PML-RARα bone marrow transduced with various MYC alleles. Data in this figure were obtained in three independent Southern blots. Thick vertical lines separate groups of samples and indicate juxtapositions of lanes. Thin vertical lines also indicate juxtaposition of lanes.